This qualitative study explores the experiences of young adults with Asperger's syndrome and their parents. Using grounded theory methodology, young adults with Asperger syndrome (n=18) aged 18-35 years and parents of young adults with Asperger's syndrome (n=23) were interviewed. Participants represented twenty-five families and a total of 42 face-to-face interviews with young adults and parents were conducted. Some interviews were carried out with young adults and parent/s together, others separately. Secondary or other data sources were used in the constant comparison of interview data, this included published personal accounts and notes taken from telephone conservations, meetings and conferences. Theoretical sampling and constant comparative analysis were the processes by which a substantive theory emerged about the phenomenon not quite fitting in -a multi-dimensional concept that offers one explanation of the varying experiences of both young adults with Asperger's syndrome and their parents. The non-obvious nature of Asperger's syndrome was central to the overall experiepce of not quitefitting in for young adults and their parents. Young adults 'looked normal' and had normal levels of intelligence but they behaved in ways that seemed 'socially inept', 'socially awkward', 'inflexible', and 'lacked empathy'. They expressed 'feeling different' from others, and had difficulty identifying a sense of 'self' in relation to others. Parents also described ways in which they did not quilefit in to normal expectations of parenting an adult son or daughter. Parents did not regard themselves, nor were they recognised by others, as 'informal carers'. Furthermore their son or daughter did not perceive themselves as being 'cared for'. Nevertheless, the data revealed a considerable amount of 'caring' involved for parents, both psychological (psychological 'watching over', companionship, managing emotions) and practical (providing shelter, food, security, money). Interestingly, this unacknowledged 'caring' was often carried out without the knowledge of young adults, and was both inadvertently and deliberately 'covert' in nature. Through the process of constant comparative analysis, the phenomenon of not quite fitting in was theorised through integrating the findings with other literatures; biographical, empirical and theoretical. Through this process, a symbolic interactionist perspective, derived from the work of G. H Mead (1934) about self and society, emerged as a framework that offered a theoretical explanation for the phenomenon of not quitefitting in. 'Me study also reflects on the many ethical and practical dilemmas of undertaking research with this particular group of participants. Finally, the study has implications for practice and further research in relation to health care professionals, such as health visitors, school nurses and family doctors, who are not specialists but who may come into contact with children and adults 'living with Asperger's syndrome', often before a diagnosis has been made. In concluding the study these implications for practice are briefly outlined for the stimulation of further thought, discussion and research.