Aggressive and criminal behavior among patients with manic and depressive conditions has been in need of greater delineation, particularly since the advent of current pharmacotherapies. This report reviews the literature on aggression and criminality among bipolar and unipolar patients and the nature and occurrence of these conditions among criminal and unprosecuted offender populations, and presents a study of 100 consecutive prisoners (89 women, 11 men) referred for psychiatric evaluation. It is hypothesized that manic and depressive states are underdiagnosed in prison populations, particularly among female prisoners. A comparatively high incidence (10%) of primary affective disorder was found in this study; possible causes of the hypothesized underdiagnosis are discussed.