Transition to adulthood, referring to the process of moving from childhood to adulthood, can be a complex period for youths with disabilities who might need special support transitioning into an independent life as adults. Caregivers are significant persons for the youths, which is why their own health and wellbeing is important. Therefore the overall aim of this thesis was to gain a deeper understanding of health and wellbeing, challenges, preferences and needs during the transition from childhood to adulthood in youths with disabilities and their caregivers. The thesis is comprised of two studies, study A focusing on the perspectives of youths with CP (Paper I) and of their caregivers (Paper II) and Study B focusing on the perspectives of immigrant youths with disabilities and caregivers from Middle Eastern countries residing in Sweden (Paper III and IV). Study A had a qualitative approach and involved focus groups and individual interviews with 12 male and female youths, 17-18 years of age, with CP and various physical and cognitive levels of disabilities (Paper I), as well as 15 mothers and fathers (Paper II). The interviews were analysed using qualitative content analysis. In Study B, a combination of qualitative and quantitative methods was used. Based on structured and semi-structured questionnaires in combination with open ended questions interviews were conducted in Swedish or Arabic with 17 male and female youths, 13-24 years of age with various disabilities and 10 mothers, five fathers and one sibling. The families were all immigrants with Middle Eastern origin and most of them had lived in Sweden for more than five years. The questionnaires Family Need Survey (FNS), Rotterdam Transition Profile (RTP) and Canadian Occupational Performance Measure (COPM) were all translated and adapted to Swedish except for COPM where there already was a Swedish version. The results were analysed using mainly descriptive statistics and based on the framework of International Classification of Functioning, Disability and Health – Children & Youth Version (ICF-CY). The findings from study A showed that the experiences of youths and caregivers mostly concerned mental health and wellbeing described as both positive and negative experiences. Their family life was experienced as important, secure and convenient, which made the youths feel safe and gave parents a sense of meaningfulness. Youths described participation, socialising and love as being important, but also challenging and worrying. Caregivers experienced sorrow and anger and together with demanding logistics, planning and worrying, their health was affected negatively during their children's transition to adulthood. The findings from study B showed that youths were dependent on their caregivers for transportations, participating in leisure activities and socialising with friends. They were also dependent on their caregivers for the demanding of support and health care. The youths had few or no experiences of intimate relationships but felt that they were expected to get married in the future which worried them and their caregivers. Caregivers were uncomfortable with using the term intellectual disability. Caregivers needed help to understand their child's condition and to explain the child's condition to their wives/husbands. A significant difference was found in what problems youths identified with and what their caregivers identified as their youth's problems. The youths experienced problems with handling finances, transportations and seeking employment or daily activities whilst their caregiver thought their youth's primary problems involved self-care. The overall finding showed that to strengthen health and wellbeing in youths with disabilities and their caregivers and to meet challenges, preferences and needs during transition from childhood to adulthood both youths and caregivers need information and support. Both youths and caregivers expressed a desire for individualised support given by one person who could facilitate the transition period by coordinating information and give support based on individual preferences and needs. During the recruiting process in both studies, great challenges were experienced in finding participants. Collaboration with professionals in schools and leisure activities was found to be the most effective way to get in contact with immigrant youths and thereby also their caregivers. The findings from this thesis may enable professionals to develop and improve best practice guidelines for support, habilitation and health care in youths' transition. To facilitate for the youth to transfer from services with a family-centred approach to person-centred adult services, their autonomy must be strengthened by involving them in their own transition planning early on. Immigrant youths need special information and support about love and the freedom of choice to get married. The COPM and RTP are suggested to be used as tools in person-centred transition planning given they are used customized and applied with cultural sensibility. To enable those with communication limitations to give their independent voice the use of communication tools is necessary. Furthermore, the transition to person-centred adult support and health care should be flexible and not determined by biological age. However, youths need support by their caregivers who in turn might both need, and want, support for themselves and occasionally hands-on support. Guidance by a specially designated navigator aimed to support the whole family would be an option to meet individual needs. The information and support should be culturally sensitive with respect to various linguistic and cultural experiences. To close the gaps between systems of care collaboration was discussed to be necessary to facilitate the transition between support and health care for children and youths as well as services for adults. The use of ICF-CY as a framework for understanding needs and the standardised terminology in ICF-CY in documentation can facilitate this collaboration.