Table 4 compares the observed prevalence rates of psychiatric disorder in drug service patients between London centres and Nottingham/Sheffield. Despite a consistent pattern of marginally higher prevalence in London centres across the spectrum of dis- orders, there is no statistically significant difference in the proportions assessed to have one or more disorder, or a disorder within any of the three main subgroups assessed (psychosis, personality disorder, affective and anxiety disorder). We imple- mented an extended multivariate analysis to assess whether there was any difference in the odds of comorbidity between the London and Nottingham/Sheffield samples after adjustment for demographic (gender, ethnicity, age) and case-mix (presence of alcohol misuse, drug use profile) variables.