Obstetric units have become larger, with patients being knowledgeable and demanding. Also, established team works at maternity wards require that midwives are secure in their role. A descriptive study with a phenomenological approach was used. A maternity unit in a hospital located in Western Sweden was chosen. Five expert midwives with vast experience of obstetric care who worked in a maternity unit were interviewed. Data were collected by audio-taped interviews. The data were analysed by means of Giorgi’s phenomenological method. The results showed that security was constituted by an inherent sense of security as well as confidence in self and in life. Education and practical group training in the workplace provided theoretical knowledge and practical experience. Support for others in the working team and open communication also constituted security. Also, clear leadership, guidelines and routines provided a framework and had a positive effect on expert midwives’ sense of security. When security was absent, midwife became worried, the joy and harmony diminished. In order to ensure midwife security and ultimately safe patient care, it was important to allow time for rest, to reflect on and evaluate their work. Expert midwives can create the prerequisites for their professional security. Several constituents combine to shape midwives’ sense of professional security; an inherent sense of security, own knowledge and experience, team collaboration, visible and clear leadership.