Most research on orthorexia nervosa (ON)-the tendency to only eat foods that are perceived as healthy-has been based on non-clinical samples. Thus, we examined prevalence of and changes in orthorexic tendencies in a large sample of inpatients with mental disorders. Cross-sectional and longitudinal associations with body weight and eating disorder (ED) symptoms were tested in subgroups of inpatients with anorexia nervosa (AN) and bulimia nervosa (BN).