This is an epidemiological and demographic study of 1285 transsexuals in the Netherlands. The data were collected from 1975 to the end of 1992. Over 95% of the Dutch transsexuals have been treated at the study center. Between 1975 and 1984 the annual number of female-to-male transsexuals increased, stabilizing thereafter. In the male-to-female transsexuals this trend continued up to 1989, declining slightly thereafter. Over the last 5 years on average 50 (range 38-60) male-to-female transsexuals and 21 (range 14-25) female-to-male transsexuals received surgical and/or hormonal treatment yearly. The sex ratio remained stable over this period: 3 male vs. 1 female subject. The calculated prevalence of transsexualism in The Netherlands is 1:11,900 males and 1:30,400 females. Transsexuals live predominantly in urbanized areas, but those living in nonurbanized areas show an even distribution over the country. The majority of female-to-male transsexuals apply for reassignment between the ages of 20-25, seldom in middle ages. The majority of male-to-female transsexuals do so between the ages of 25-30 and middle-aged subjects are not rare. Between 77-80% of both categories receive surgical and/or hormonal treatment. Five male-to-female transsexuals regretted sex reassignment.