In a retrospective study of anorexia nervosa and bulimia nervosa, potential cases were traced, studied, and diagnosed according to ICD-10. Forty-two cases were found in Bornholm County, comprising the island of Bornholm in Denmark, in a population of 47,000 from 1970 to 1989. Less than half of these cases (n = 16) were registered in Danish psychiatric case registers, and 35% (n = 14) could be found only by search in primary care. The incidence rates were stable during most of the study period, but a significant increase occurred during the last 5 years. The prevalence rates, determined by counting the number of cases in the population year by year, also increased during the late part of the study period. In 1989 the incidence rate of the high-risk group of females 10 to 24 years of age was 136 per 100,000 for anorexia nervosa and 45 per 100,000 for bulimia nervosa, and the prevalence rate was 222 per 100,000 for anorexia nervosa and 89 per 100,000 for bulimia nervosa.