Objective: The purpose of this study was to determine the treatment history and cost of previous treatment among patients with comorbid substance-related disorder and dysthymia, as compared to patients with substance-related disorder only. Method: Retrospective data were obtained regarding past treatment. Treatment cost was calculated on the basis of the 1996 cost of various treatment modalities. The setting was alcohol-drug programs located within departments of psychiatry in two centers. A total of 642 patients were assessed, of whom 39 had substance-related disorder and dysthymia and 308 had substance-related disorder only (the remaining patients had other comorbid conditions). Data collection instruments included an interview-based questionnaire regarding previous psychiatric and substance abuse treatment. Current cost of treatment in various settings was assessed on the basis of a survey of facilities used by patients in this area. Results: Patients with substance-related disorder and dysthymia had received more substance-related disorder treatment in 18 of 20 measures. Patients with substance-related disorder and dysthymia used 4.7 times more substance- related disorder treatment dollars than patients with substance-related disorder only, although their demographic characteristics were similar. Past self-help activities and pharmacotherapy were remarkably similar for both groups. Although substance-related disorder treatment differed considerably between the two groups of patients, other types of psychiatric treatment (i.e., non-substance-related treatment) did not differ between the two groups. Conclusions: Patients with substance-related disorder and dysthymia are referred to (or seek) substance-related disorder treatment more often than patients with substance-related disorder only but are referred to (or seek) non-substance-related psychiatric treatment no more often than patients with substance-related disorder only. The cost of previous substance-related disorder treatment was several times higher for the patients with substance- related disorder and dysthymia.