Of 106 patients attending a gender-identity clinic, 73% satisfied DSM–III criteria for transsexualism. These DSM–III positives had a significantly younger age of onset and were less likely to experience sexual arousal with cross-dressing than those who did not satisfy DSM–III criteria. They were also significantly more likely to fulfil a definition of ‘core transsexualism’. ‘Core transsexualism’ may represent a subgroup within DSM–III criteria for transsexualism and its defining features in this study were an early age of onset, low sexual activity, lack of sexual arousal with cross-dressing and homosexual orientation. Of the whole sample, 23% were referred for gender reassignment surgery, of whom 100% were DSM–III positive and 60% were ‘core transsexuals'.