['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.', '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.', '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.'] Are grade 4 events as important as AIDS events in the era of HAART?