This study examines clinical features of late onset anorexia nervosa. This involved the scrutiny of a large database of patients with anorexia nervosa comprising data gathered at standardized initial assessments over the period 1960-1990. Patients with a late onset were compared to other selected patient samples. The population comprised 12 patients with a first onset of anorexia nervosa at or after the age of 30, 415 patients with an onset after 15 but before 20 and 9 patients with an onset after 15 but before 20 and matched for age at presentation with the late onset group. Features studied included age at menarche, age at onset of anorexia nervosa, age at presentation, duration of illness, weight at presentation, lowest adult weight, highest weight, weight at onset of illness, marital status and parity. Patients with an onset of anorexia nervosa after the age 30 comprised 2% of the total female patient sample. Though such patients were rare, their clinical features were very similar to those of typical patients with adolescent onset. Notably, young and late onset patients had similar durations of illness prior to presentation, and similar proportions had bulimia and defensive vomiting. Feared sexuality, no longer necessary for childbearing, emerged as being of apparent aetiological significance in the late onset group, with the disorder embodying its rejection, as often also seems to be the case with earlier onset. The late onset cases were hard to diagnose and had a poor outcome. The study underlines the importance of considering the diagnosis of anorexia nervosa in older patients, even if there is no earlier history of anorexia nervosa. Such patients are likely to find it easier to conceal the psychological origins of their problem behind the possibility of a primary physical illness, or behind psychiatric diagnoses such as depression, the treatment of which may not threaten their avoidance of normal body weight.