Research on many mental disorders conducted since the 1990s strongly suggests a biological component to etiology. These developments should inform the decisions clinical social workers make regarding their interventions with clients. Several recent research reports, however, suggest that social workers may underestimate the influence of biological factors in some mental disorders. Because the measures of practitioners' views developed for those studies were not sensitive to disorder-specific responses for a range of mental illnesses, the usefulness of their findings may be questioned. The authors present the results of a national study of social workers in which disorder-specific measures of mental illness were used to determine more dearly whether social workers are making research-based assessments of mental illnesses etiology. It was found that social workers attribute causality of four disorders in a manner consistent with current research.