OBJECTIVE: To estimate incidence and predictors of serious or life-threatening events that are not AIDS defining, AIDS events, and death among patients treated with highly active antiretroviral therapy (HAART) in the setting of 5 large multicenter randomized treatment trials conducted in the United States. METHODS: Data were analyzed from 2,947 patients enrolled from December 1996 through December 2001. All patients were to receive antiretrovirals throughout follow-up. Data collection was uniform for all main outcome measures: serious or life-threatening (grade 4) events, AIDS, and death. RESULTS: During follow-up, 675 patients experienced a grade 4 event (11.4 per 100 person-years); 332 developed an AIDS event (5.6 per 100 person-years); and 272 died (4.6 per 100 person-years). The most common grade 4 events were liver related (148 patients, 2.6 per 100 person-years). Cardiovascular events were associated with the greatest risk of death (hazard ratio = 8.64; 95% CI: 5.1 to 14.5). The first grade 4 event and the first AIDS event were associated with similar risks of death, 5.68 and 6.95, respectively. CONCLUSIONS: Grade 4 events are as important as AIDS events in the era of HAART. To adequately evaluate the impact of HAART on morbidity, comorbidities and other key factors must be carefully assessed.