Only Scandinavian investigators have reported on demographic aspects of reactive psychoses. Data from the National Health Service, Denmark, for age at first admission, sex, and length of stay in hospital in reactive, manic-depressive and schizophrenic psychoses are analysed. Differences in sex incidence ratios, age at first admission and length of stay are evident between the three psychoses. The differences noted are considered to provide indirect evidence supporting the separate diagnostic categories.