Background Medication nonadherence is a known risk factor for adverse outcomes in the general population. However, little is known about the association of predialysis medication adherence among patients with advanced chronic kidney disease and mortality following their transition to dialysis. Study Design Observational study. Setting & Participants 32,348 US veterans who transitioned to dialysis during 2007 to 2011. Predictors Adherence to treatment with cardiovascular drugs, ascertained from pharmacy database records using proportion of days covered (PDC) and persistence during the predialysis year. Outcomes Post–dialysis therapy initiation all-cause and cardiovascular mortality, using Cox models with adjustment for confounders. Results Mean age of the cohort was 72 ± 11 (SD) years; 96% were men, 74% were white, 23% were African American, and 69% had diabetes. During a median follow-up of 23 (IQR, 9-36) months, 18,608 patients died. Among patients with PDC > 80%, there were 14,006 deaths (mortality rate, 283 95% CI, 278-288/1,000 patient-years); among patients with PDC > 60% to 80%, there were 3,882 deaths (mortality rate, 294 95% CI, 285-304/1,000 patient-years); among patients with PDC ≤ 60%, there were 720 deaths (mortality rate, 291 95% CI, 271-313/1,000 patient-years). Compared with patients with PDC > 80%, the adjusted HR for post–dialysis therapy initiation all-cause mortality for patients with PDC > 60% to 80% was 1.12 (95% CI, 1.08-1.16), and for patients with PDC ≤ 60% was 1.21 (95% CI, 1.11-1.30). In addition, compared with patients showing medication persistence, adjusted HR risk for post–dialysis therapy initiation all-cause mortality for patients with nonpersistence was 1.11 (95% CI, 1.05-1.16). A similar trend was detected for cardiovascular mortality and in subgroup analyses. Limitations Large number of missing values; results may not be generalizable to women or the general US population. Conclusions Predialysis cardiovascular medication nonadherence is an independent risk factor for postdialysis mortality in patients with advanced chronic kidney disease transitioning to dialysis therapy. Further studies are needed to assess whether interventions targeting adherence improve survival after dialysis therapy initiation.