Objective: The aim of this study was to examine early signs of psychosis in patients suffering from both drug dependence and schizophrenia, compared to a control group of drug-addicted patients without a comorbid psychotic disorder, and to assess whether the presence of these signs was related to changes in the pattern of substance abuse.Method: In a rehabilitation hospital for young addicts, 32 patients with a comorbid diagnosis of schizophrenia and 30 patients without the diagnosis of a psychotic disorder, were assessed using the Interview for the Retrospective Assessment of the Onset of Schizophrenia. Information relating to 64 signs of early psychosis was collected from every patient. From the 64 signs, five groups of symptoms were defined: non-specific and precursor symptoms; non-specific and depressive symptoms; negative symptoms; positive symptoms; and impaired social adjustment. The semiquantitative pattern of substance abuse for each 1-year interval over the previous 10 years was investigated using the categories of chapter F1 of ICD-10 and including an additional category 'biological drugs'. The relationship between the pattern of substance abuse and the presence of early signs was assessed using anova and non-parametric statistical methods.Results: The results indicate that the defined pathological symptomatology greatly influences the pattern of consumption of psychoactive substances in both the psychosis group and the control group. The group factor exerted the greatest influence within the categories 'biological drugs' and 'other stimulants', where the 'psychosis and addiction group' consumed significantly more than the control group.Conclusions: There is a subgroup of non-psychotic addicted patients whose pattern of psychoactive substance abuse is similar to that found in addicted patients suffering from schizophrenia. It may be helpful to systematically identify this subgroup with regard to possible therapeutic implications, particularly with regard to possible pharmacological treatment options.