BACKGROUND: Although there has been considerable research into the genotype and phenotype of Williams syndrome, there have been relatively few studies of long-term prognosis. As a preliminary to a more detailed investigation of adults with Williams syndrome, a parental questionnaire was distributed to members of the UK Williams Syndrome Foundation, focusing on areas of skill and difficulties in adult life. METHOD: A postal questionnaire was distributed to all members of the UK Williams Syndrome Foundation who had a son or daughter aged 18years or over. The questionnaire covered issues related to the physical and mental health of the adults with Williams syndrome, together with questions about educational and employment status, self-help and independence skills. RESULTS: Out of a total of 290 questionnaires distributed, 239 were returned (82% response rate). The data highlighted the continuing high rates of physical problems in this group and apparent increases in rates of mental health problems with age. Parents also expressed their concerns about the lack of adequate support and care. Educational and employment attainments were generally low and self-help skills were relatively poor. DISCUSSION: The findings highlight the need for far better understanding of conditions such as Williams syndrome among professionals working in adult services and the need for more adequate support from educational, health and social services.