Background Variation in outcomes by race/ethnicity in adults with heart failure (HF) has been previously observed. Identifying factors contributing to these variations could help target interventions. We evaluated the association of race/ethnicity with HF outcomes and potentially contributing factors within a contemporary HF cohort. Methods and Results We identified members of Kaiser Permanente Northern California, a large integrated healthcare delivery system, who were diagnosed with HF between 2012 and 2016 and had at least 1 year of prior continuous membership and left ventricular ejection fraction data. We used Cox regression with time-dependent covariates to evaluate the association of self-identified race/ethnicity with HF or all-cause hospitalization and all-cause death, with backward selection for potential explanatory variables. Among 34 621 patients with HF, compared with White patients, Black patients had a higher rate of HF hospitalization (adjusted hazard ratio [HR], 1.28; 95% CI, 1.18-1.38) but a lower rate of death (adjusted HR, 0.78; 95% CI, 0.72-0.85). In contrast, Asian/Pacific Islander patients had similar rates of HF hospitalization, but lower rates of all-cause hospitalization (adjusted HR, 0.89; 95% CI, 0.85-0.93) and death (adjusted HR, 0.75; 95% CI, 0.69-0.80). Hispanic patients also had a lower rate of death (adjusted HR, 0.85; 95% CI, 0.80-0.91). Sensitivity analyses showed that effect sizes for Black patients were larger among patients with reduced ejection fraction. Conclusions In a contemporary and diverse population with HF, Black patients experienced a higher rate of HF hospitalization and a lower rate of death compared with White patients. In contrast, selected outcomes for Asian/Pacific Islander and Hispanic patients were more favorable compared with White patients. The observed differences were not explained by measured potentially modifiable factors, including pharmacological treatment. Future research is needed to identify explanatory mechanisms underlying ongoing racial/ethnic variation to target potential interventions.