Utilizing a prospective study of health service activity for HIV/AIDS, 2 estimates of hospital costs of care analysed with reference to gender, risk activity, immunological and clinical staging (1987 definition of AIDS) were undertaken. Utilizing combined costs per life year (based on hospital and hospice activity but not primary and community care) the ratio of costs for CD4 < 200 and CD4 > 200 was for most risk groups between 2-5:1 whilst for AIDS: pre-AIDS it was between 3.6-8.3:1 except for homosexuals where it was 12.6:1. A comparison of the standard hospital costs for infectious diseases with the published accounts for clinical AIDS care in Lothian suggests a 3-4-fold underestimate in the costs of providing a comprehensive health care service.