In order to describe the clinical features of AIDS, particularly injection drug use (IDU) related AIDS in patients attending the Regional Infectious Diseases Unit in Edinburgh a prospective review of the 680 HIV-positive patients, 30% of whom were women and 68% were infected via IDU was undertaken. The commonest AIDS-related clinical problem in Edinburgh was Pneumocystis carinii pneumonia (PCP). Whilst gender differences were not apparent in terms of clinical problems, differences were observed in risk groups as previously reported; Kaposi's sarcoma (KS), cytomegalovirus (CMV) and toxoplasmosis were commoner in homo/ bisexuals whilst oesophageal candidiasis was commoner in drug users. Extrapulmonary tuberculosis was uncommon unlike cohorts from the USA or Italy. Each patient with AIDS can expect 1-2 AIDS-related clinical events per year of survival. Considerable differences in mortality rates by risk group but not by gender were observed and explanations for this difference need to be considered further. The mortality rates for drug users were however remarkably similar to published rates from Amsterdam and the Bronx, New York.