This study was intended to establish the pathogenic significance of sport and exercise in the development of eating disorders. Hospitalized eating disordered patients and an age-matched control group were assessed. Historical and current physical activity data were collected. An indepth interview was also conducted to ascertain the age of onset of the diagnostic symptoms for eating disorders, and to determine whether: (i) exercising predated dieting; (ii) patients had been involved in competitive athletics; (iii) exercise was excessive; and (iv) weight loss was inversely related to level of exercise. The results indicated that patients were more physically active than controls from adolescence onwards, and prior to the onset of the primary diagnostic criteria for anorexia nervosa. A content analysis of the interview data indicated that 78% of patients engaged in excessive exercise, 60% were competitive athletes prior to the onset of their disorder, 60% reported that sport or exercise pre-dated dieting, and 75% claimed that physical activity levels steadily increased during the period when food intake and weight loss decreased the most. Together our results suggest that overactivity should not be routinely viewed as a secondary symptom in anorexia nervosa, equivalent to other behaviours. For a number of anorexic women, sport/exercise is an integral part of the pathogenesis and progression of self-starvation.