Introduction and Aims. This paper describes the sociodemographic characteristics of 196 psychotic patients admitted to acute psychiatric wards in the UK, Denmark, Germany and Italy, with the aim of comparing comorbid with non-comorbid patients. Design and Methods. It is a prospective field study with repeated measures at 1, 6 and 12 months. Patients were recruited from acute psychiatric wards in four European centres. They were grouped as comorbid or not on the basis of urine analysis. The Schedules for Clinical Assessment in Neuropsychiatry was used to provide a psychiatric diagnosis, and the Positive and Negative Symptom Severity Scale for further information on specific symptoms with results from the Fragerstrom test for nicotine dependence also reported. Results. Comorbid patients were younger than those who were not but did not differ significantly in the other sociodemographic measures. Differences in sociodemographic characteristics of patients between centres were apparent. Comorbid patients had higher levels of positive and lower levels of negative symptoms than those who were non-comorbid. Differences were found in the patterns of drug use between comorbid patients who were using cannabis compared with those who were not. Discussion and Conclusions. Cross-cultural differences in the sociodemographic characteristics of the comorbid patient population give us a better insight into this heterogenous group. [Baldacchino A, Blair H, Scherbaum N, Grosse-Vehne E, Riglietta M, Tidone L, Criaco C, Marelli MC, Sommer B, Tan L, Little H, Ghodse H. Drugs and Psychosis Project: A multi-centre European study on comorbidity. Drug Alcohol Rev 2009;28:379-389].