This study evaluates the prevalence of threshold and subthreshold use of substances among patients with psychiatric disorders and 2 comparison groups. Participants were outpatients and inpatients with mood and anxiety disorders, subjects with opiate dependence, and a comparison group of individuals not undergoing treatment for psychiatric disorders. Assessments included the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition , Axis I Disorders, an interview exploring the spectrum of substance use (Structured Clinical Interview for the Spectrum of Substance Use), and a self-report instrument exploring the spectrum of 5 psychiatric disorders (General 5-Spectrum Measure). The overall frequency of substance use disorder (SUD) and that of subthreshold use were 46% and 8% in patients with bipolar disorder, 4% and 26% in those with panic disorder, 8% and 26% in those with obsessive-compulsive disorder, and 6% and 10% in the control group, respectively ( Idouble dagger 2 = 51.6, P < .001). Inspection of standardized residuals indicated that alcohol use disorder and SUD were significantly ( P < .05) more frequent in subjects with bipolar disorder than among those with obsessive-compulsive disorder or panic disorder. The latter showed a significantly higher subthreshold use of substances than control subjects. The pattern of motivations for use varied according to the psychiatric disorder. Our results suggest that the well-established relationship between SUDs and psychiatric disorders might be the end point of a process that starts from increased proneness to substance use, which first leads to self-medication and then may eventually develop into substance abuse or dependence, among subjects with psychiatric symptoms.