A review of the literature revealed that there was no adequate assessment instrument available that screens comprehensively for anxiety and depression in persons with mental retardation. The purpose of this research was to develop the Anxiety, Depression, and Mood Scale (ADAMS), an instrument intended to fill this gap. We developed a preliminary rating scale that included 55 symptom items. We examined the factor structure of these items by an exploratory factor analysis of behavior ratings on 265 individuals. A five-factor solution emerged that was both statistically sound and clinically meaningful. These factors were labeled "Manic/Hyperactive Behavior," "Depressed Mood," "Social Avoidance," "General Anxiety" and "Compulsive Behavior." We validated this solution by conducting a confirmatory factor analysis on ratings of 268 additional individuals. Model fit was acceptable. Internal consistency of the subscales and retest reliability for both the total scale and the subscales was high. Interrater reliability was satisfactory. The validity of the ADAMS was assessed with a clinical sample of 129 individuals with mental retardation who were seen in a psychiatric clinic; this provided additional support for the subscales. The ADAMS appears to be a psychometrically sound instrument for screening anxiety, depression and mood disorders among individuals with mental retardation.