The aim of the present study was to demonstrate what far-reaching consequences dieting may produce in teenage girls and to determine whether there is a direct relation between dieting and the development of anorexia nervosa. The study took the form of a longitudinal prospective investigation of dieting teenage schoolgirls over a 10-year observation period, particularly as regards physical and mental state of health and general psychosocial development. The questionnaire study underlying the present work--entitled "The feeling of being fat and dieting in a school population"--was published in 1971 by Ingvar Nylander. With the aim of determining how often teenagers feel overweight, how often they diet and how often they develop disorders from dieting, Nylander interviewed 2370 students (1129 boys and 1241 girls). His study was published in Acta Socio-Medica Scand 1971, 1. In the present work a primary material of 130 girls was selected from the dieting schoolgirls and 111 of these were examined by the author. The methods included a personal interview, examination of physical and mental health, an EEG examination and an intelligence test. Moreover, information was obtained concerning the subjects from their parents and from school health records and hospital case records. A follow-up study was done 10 years later, in which 97 of the subjects were again examined by the author while 12 subjects merely answered a questionnaire. The methods used were very similar to the foregoing ones. The subjects' dieting behaviour was evaluated on the basis of an anorectic behaviour scale. Further information was obtained from hospital case records. The overall situation of the subjects was evaluated on the basis of case histories and of data from case records concerning heredity, environment, psychosocial adjustment, state of health and findings on examination. Some of the subjects had had a dieting problem for a long time; they had generally dieted for short but repeated periods, but, in most cases, with little effect on their weight. Some patients had developed anorectic behaviour, or even AN, others did not. The former group had shown such behaviour at an early stage--or other signs of mental insufficiency--while the latter group was healthy and during dieting periods developed neither anorectic behaviour nor anorexia nervosa. Thus no direct causal relation between dieting and anorexia nervosa could be demonstrated. If dieting is caused by mental insufficiency, this may lead to the development of anorectic behaviour and/or anorexia nervosa.(ABSTRACT TRUNCATED AT 400 WORDS)