As part of an ongoing scale development process, this study provides an initial examination of the psychometric properties and validity of a new interview-based negative symptom instrument, the Clinical Assessment Interview for Negative Symptoms (CAINS), in outpatients with schizophrenia or schizoaffective disorder (N = 37). The scale was designed to address limitations of existing measures and to comprehensively assess five consensus-based negative symptoms: asociality, avolition, anhedonia (consummatory and anticipatory), affective flattening, and alogia. Results indicated satisfactory internal consistency reliability for the total CAINS scale score and promising inter-rater agreement, with clear areas identified in need of improvement. Convergent validity was evident in general agreement between the CAINS and alternative negative symptom measures. Further, CAINS subscales significantly correlated with relevant self-report emotional experience measures as well as with social functioning. Discriminant validity of the CAINS was strongly supported by its small, non-significant relations with positive symptoms, general psychiatric symptoms, and depression. These preliminary data on an early beta-version of the CAINS provide initial support for this new assessment approach to negative symptoms and suggest directions for further scale development.