Receptors of the 5-HT2C subtype are assumed to be involved in the influence of serotonin on food intake. A polymorphism in the coding region of the gene for this receptor, resulting in a cysteine to serine substitution, has been reported. Fifty-seven somatically healthy teenage girls displaying weight loss and 91 normal-weight girls of the same age, all recruited by means of a population-based screening study, were compared with respect to this polymorphism. Subjects in the weight loss group displayed a higher frequency of the serine allele than those in the comparison group (23.7% vs. 7.7%, p =.0001). Seventy-two percent of the weight loss girls fulfilled the diagnostic criteria of anorexia nervosa, whereas 28% did not; when these two groups were separately analyzed, both differed significantly from controls with respect to serine allele frequency. The results support the notion that the studied gene may be involved in the regulation of food intake in young women.