The aim of this article is to examine the onset and clinical correlates of substance use in patients with psychotic disorders. One hundred and eight inpatients and outpatients with DSM-IV psychotic disorders were evaluated with the SCI-SUBS, an instrument designed to explore the spectrum of substance use and its clinical correlates. Comparisons were made between subjects with (n=47) and without (n=61) a DSM-IV diagnosis of substance use disorder (SUD). In patients with an early onset of psychosis (