The objective of this study was to compare the features of female-to-male transsexuals (F-M) with those of male-to-female transsexuals (M-F) in the cohort of all applicants for sex reassignment over a 20-year period. In an observational, cross-sectional design the cohort was retrospectively identified, consisting of all 233 subjects who applied for sex reassignment in Sweden during the period 1972-1992. The cohort was subdivided into the groups M-F (n=134) and F-M (n=99), and the two groups were compared. M-F were older when applying for sex reassignment surgery than F-M, and more often had a history of marriage and children than their F-M counterparts. M-F also had more heterosexual experience. F-M, on the other hand, more frequently exhibited cross-gender behaviour in childhood than did M-F transsexuals. The present and previous studies strongly support the view that transsexualism manifests itself differently in males and females. Various models for understanding these differences are discussed.