There is growing interest in deficit symptoms in studies of the course and treatment response of schizophrenia. However, existing clinical assessment instruments focus primarily on productive symptoms. The authors describe the Quality of Life Scale (QLS), a 21-item scale based on a semistructured interview designed to assess deficit symptoms and thereby fill an important gap in the range of instruments now available. Data regarding reliability and training in the use of the QLS are presented. A factor analysis of the items yields results compatible with the conceptual model on which the scale is based. The factor analysis was also performed separately by sex and was fundamentally similar for men and women.