543 persons in AIDS risk groups were examined for LAV/HTLV-III infection. Antibodies against LAV/HTLV-III were demonstrated in 377, during an observation period of 3 months to 3 years. Patients were divided into 5 groups, according to clinical, serological and immunological criteria. Severity of symptoms and incidence of recurrences of the lymphadenopathy syndrome correlated positively with an increase in cellular immune deficiency. At the end of the observation period only 30 of 307 antibody-positive patients were well. The AIDS incidence of all antibody-positive patients increased with time from 3% (6-11 months) to 19.4% (24-36 months). If one takes into account only those patients who had marked immune deficiency (stage 2b) at the initial examination, the AIDS incidence during the same periods was 10 and 57%, respectively. At the same time, the condition worsened by at least one stage in half of all patients in stages 1b-2a observed for 1-2 years. A change of stage was observed in up to 80% of patients followed for longer periods. Long-time prognosis of LAV/HTLV-III infection is remarkably bad.