IMPORTANCE: Geographic, racial, and ethnic variations in quality of care and outcomes have been well documented among the Medicare population. Few data exist on beneficiaries living in Puerto Rico, three-quarters of whom enroll in Medicare Advantage (MA). OBJECTIVE: To determine the quality of care provided to white and Hispanic MA enrollees in the United States and Puerto Rico. DESIGN, SETTING, AND PARTICIPANTS: A cross-sectional study of MA enrollees in 2011 was conducted, including white enrollees in the United States (n = 6 289 374), Hispanic enrollees in the United States (n = 795 039), and Hispanic enrollees in Puerto Rico (n = 267 016). The study was conducted from January 1, 2011, to December 31, 2011; data analysis took place from January 19, 2015, to January 2, 2016. MAIN OUTCOMES AND MEASURES: Seventeen performance measures related to diabetes mellitus (including hemoglobin A1c control, retinal eye examination, low-density lipoprotein cholesterol control, nephropathy screening, and blood pressure control), cardiovascular disease (including low-density lipoprotein cholesterol control, blood pressure control, and use of a ß-blocker after myocardial infarction), cancer screening (colorectal and breast), and appropriate medications (including systemic corticosteroids and bronchodilators for chronic obstructive pulmonary disease [COPD] and disease-modifying antirheumatic drugs). RESULTS: Of the 7.35 million MA enrollees in the United States and Puerto Rico in our study, 1.06 million (14.4%) were Hispanic. Approximately 25.1% of all Hispanic MA enrollees resided in Puerto Rico, which was more than those residing in any state. For 15 of the 17 measures assessed, Hispanic MA enrollees in Puerto Rico received worse care compared with Hispanics in the United States, with absolute differences in performance rates ranging from 2.2 percentage points for blood pressure control in diabetes mellitus (P = .03) to 31.3 percentage points for use of disease-modifying antirheumatic drug therapy (P < .01). Adjusted performance differences between Hispanic MA enrollees in Puerto Rico and Hispanic MA enrollees in the United States exceeded 20 percentage points for 3 measures: use of disease-modifying antirheumatic drug therapy (-23.8 percentage points [95% CI, -30.9 to -16.8]), use of systemic corticosteroid in COPD exacerbation (-21.3 percentage points [95% CI, -27.5 to -15.1]), and use of bronchodilator therapy in COPD exacerbation (-22.7 percentage points [95% CI, -27.7 to -17.6]). CONCLUSIONS AND RELEVANCE: We found modest differences in care between white and Hispanic MA enrollees in the United States but substantially worse care for enrollees in Puerto Rico compared with their US counterparts. Major efforts are needed to improve care delivery on the island to a level equivalent to the United States.