Background: A contextual understanding of hypertension control can inform population health management strategies to mitigate cardiovascular disease events. This retrospective cohort study links neighborhood-level data with patients’ health records to describe racial/ethnic differences in uncontrolled hypertension and determine if and to what extent these differences are mediated by neighborhood socioeconomic status (nSES). Methods: We conducted a mediation analysis using a sample of patients with hypertension from 2 health care delivery systems in San Francisco over 2 years (n=47 031). We used generalized structural equation modeling, adjusted for age, sex, and health care system, to estimate the contribution of nSES to disparities in uncontrolled hypertension between White patients and Black, Hispanic/Latino, and Asian patients, respectively. Sensitivity analysis removed adjustment for health care system. Results: Over half the cohort (62%) experienced uncontrolled hypertension during the study period. Racial/ethnic groups showed substantial differences in prevalence of uncontrolled hypertension and distribution of nSES quintiles. Compared with White patients, Black, and Hispanic/Latino patients had higher adjusted odds of uncontrolled hypertension: odds ratio, 1.79 [95% CI, 1.67–1.91] and odds ratio, 1.38 [95% CI, 1.29–1.47], respectively and nSES accounted for 7% of the disparity in both comparisons. Asian patients had slightly lower adjusted odds of uncontrolled hypertension when compared with White patients: odds ratio, 0.95 [95% CI, 0.89–0.99] and the mediating effect of nSES did not change the direction of the relationship. Sensitivity analysis increased the proportion mediated by nSES to 11% between Black and White patients and 13% between Hispanic/Latino and White patients, but did not influence differences between Asian and White patients. Conclusions: Among patients with hypertension in this study, nSES mediated a small proportion of racial/ethnic disparities in uncontrolled hypertension. Population health management strategies may be most effective by focusing on additional structural and interpersonal pathways such as racism and discrimination in health care settings.