Objective: The authors assessed reliability and validity of a scale developed for use with inpatients on a mood disorders unit. The scale is used to rate a patient's mood along a quantitative continuum from -5, depressive stupor, through 0, eutbymic, to 5, full mania. The scale lists behaviors that constitute criteria for each rating point. Mixed states and idiosyncratic behavior can also be assessed. Methods: Assessment of the scale's reliability and validity was based on data for 53 psychiatric inpatients. The scale's reliability was assessed by comparing nurses' ratings. Validity was assessed by comparing nurses' ratings with patients' selfratings using previously validated self-report instruments as well as a patient self-report version of the scale. Results: Interrater reliability for the instrument was high (r=.84). Estimates of validity obtained using patient self-report measures ranged from .54 to .85. Conclusions: The psychometric properties of the scale are comparable to and in some cases are superior to those reported for instruments that include more items and that take longer to complete.