The author used a scale that emphasizes objective behavioral signs to evaluate affective flattening and to rate affect in 69 patients suffering from schizophrenia (N = 30), mania (N = 19), and depression (N = 20). Raters were blind to the patient's diagnosis. Interrater reliability was assessed and found to be adequate to good for most items on the scale and for a global rating. The affective flattening was found to be common, but not omnipresent, in schizophrenia; it was also common among the depressed patients. The author recommends that affective flattening be considered as an important criterion for schizophrenia and that future research explore its frequency and prognostic significance.