Examined the factor structure of the Profile of Mood States (POMS) in samples of psychiatric outpatients (N = 165) and adult smokers (N = 298). Principal component analyses (oblique rotation) yielded seven interpretable components in both cases, which accounted for 66% and 64% of the total variance, respectively. Coefficients of congruence indicated that the two component structures were quite similar. Three of the six POMS scales (Anger-Hostility, Vigor-Activity, Fatigue-Inertia) were replicated successfully in both samples. The remaining three scales were factorally complex and tended to merge, partially attributable to social desirability, to high scale intercorrelations, and to the inherent confluence of psychopathology. The POMS appears to be an internally consistent, multidimensional instrument with a relatively stable factor structure. Caution is recommended in the separate scoring and interpretation of several POMS scales.