A retrospective study of typical 24-h food intake was undertaken of the diets of 17 anorexia nervosa patients during the initial and the most severe phases of their illness. Patients completed a nutritional knowledge questionnaire. Patients' diets were significantly lower in energy and in all major nutrients than those of control subjects. The proportion of energy derived from protein was significantly higher, from fats significantly lower and from carbohydrates not significantly different from that of controls. The mean intake of all nutrients in the more severe phase of illness was lower in the initial phase. Intakes of calcium, retinol activity and ascorbic acid were below RDA levels in the majority of patients, but only a few reported intakes of thiamin, riboflavin and niacin equivalent below RDA values. Most patients scored higher on the nutritional knowledge questionnaire than matched controls, particularly in respect to questions concerning caloric content of food, dieting and roughage. Not all patients obtained high nutritional knowledge scores however, and 25 per cent performed less well than selected controls.