The authors explored the binge eating symptomatology in 74 patients receiving clozapine (N = 57) or olanzapine (N = 17), and compared body mass index (BMI, kg/m(2)) and weight gain in patients with and without binge eating symptomatology. Subjects who screened positively for binge eating were interviewed using a modified version of the Questionnaire on Eating and Weight Patterns (QEWP). Current BMIs were assessed cross-sectionally, BMIs at initiation of clozapine/olanzapine treatment retrospectively. Thirty-seven subjects (50%) screened positively. Taking clozapine and olanzapine together, 6/27 (22.2%) females and 3/47 (6.4%) males fulfilled criteria for binge eating disorder, 3/27 (11.1%) females and 2/47 (4.3%) males for bulimia nervosa. Patients who screened positively showed higher current BMIs (26.8 +/- 3.9 vs. 24.7 +/- 3.7 kg/m(2)) and higher BMI increments during clozapine/olanzapine treatment (3.9 +/- 3.1 vs. 2.6 +/- 3.4 kg/m(2)) than patients who screened negatively. We conclude that clozapine/olanzapine may induce binge eating and full blown eating disorders which may have predictive value for weight gain. For future research in this field we suggest a novel DSM-IV research classification "Medication-induced eating disorders".