The purpose of the study is to explore particular challenges faced when designing virtual environments for children with autism, with the purpose of training social skills. Our findings are based on studying autistic behaviour during three years (primary and secondary sources), analysis of related system and other computer mediated assistive technology, as well as general game design. From these studies we have identified eight critical design parameters that need to be adjustable in a system suitable for autistic persons. The parameters importance, their variation range, as well as the need for independent adjustment of these were estimated and verified by experienced expert pedagogues.