Whether earlier initiation of RRT in critically ill patients with AKI can improve outcomes remains debated. We examined follow-up data from a large clinical trial to prospectively investigate the long-term outcomes associated with the timing of RRT initiation in such patients. We extended the follow-up of patients in the Early Versus Delayed Initiation of RRT in Critically Ill Patients with AKI (ELAIN) Trial from 90 days to 1 year after randomization for 230 (99.6%) patients. The primary outcome was a composite of major adverse kidney events (persistent renal dysfunction, dialysis dependence, and mortality) at 1 year. Secondary outcomes included inflammatory markers. Overall, 72 of 111 (64.9%) and 106 of 119 (89.1%) patients met the primary outcome in the early (stage 2 AKI) and delayed (stage 3 AKI) initiation groups, respectively (odds ratio [OR] with early initiation, 0.23; 95% confidence interval [95% CI], 0.11 to 0.45; P< 0.001). The early initiation group had a 1-year all-cause mortality rate (56 of 111 [50.2%]) significantly lower than that of the delayed initiation group (83 of 119 [69.8%]; absolute difference, -19.6%; 95% CI, -32.0% to -7.2%; P<0.01). After 1 year, 16 of 55 (29.1%) and 23 of 36 (63.9%) surviving patients in the early and delayed groups, respectively, failed to recover renal function (absolute difference, -34.8%; 95% CI, -54.6% to -15.0%; P=0.001). In conclusion, early initiation of RRT in these critically ill patients with AKI significantly reduced the occurrence of major adverse kidney events, reduced mortality, and enhanced renal recovery at 1 year.