Background Persons of African-Caribbean origin are more frequently imprisoned, and increasing evidence suggests they are detained more frequently in psychiatric hospitals, following offending behaviour. Aims To estimate population-based prevalence rates of treated mental disorder in different ethnic groups compulsorily admitted to secure forensic psychiatry services. Method A survey was recorded of 3155 first admissions, from 1988 to 1994, from half of England and Wales, with 1991 census data as the denominator adjusted for under-enumeration. Results Compulsory admissions for Black males were 5.6 (Cl 5.1-6.3) times as high as, and for Asian males were half, those for White males; for Black females, 2.9 (Cl 2.4-4.6) times as high and for Asian females one-third of those for White females. Admissions of non-Whites rose over the study period. Patterns of offending and diagnoses differed between ethnic groups. Conclusions Variations in compulsory hospitalisation cannot be entirely attributed to racial bias. Community-based services may be less effective in preventing escalating criminal and dangerous behaviour associated with mental illness in African-Caribbeans. Declaration of interest None. Funding was provided by the Department of Health.