BACKGROUND:It has been observed that married cancer patients have lower mortality rates than unmarried patients, but data for different racial/ethnic groups are scarce. The authors examined the risk of overall mortality associated with marital status across racial/ethnic groups and sex in data from the California Cancer Registry. METHODS:California Cancer Registry data for all first primary invasive cancers diagnosed from 2000 through 2009 for the 10 most common sites of cancer-related death for non-Hispanic whites (NHWs), blacks, Asians/Pacific Islanders (APIs), and Hispanics were used to estimate multivariable hazard ratios (HRs) and 95% confidence intervals (CIs) for marital status in relation to overall mortality by race/ethnicity and sex. The study cohort included 393,470 male and 389,697 female cancer patients and 204,007 and 182,600 deaths from all causes, respectively, through December 31, 2012. RESULTS:All-cause mortality was higher in unmarried patients than in married patients, but there was significant variation by race/ethnicity. Adjusted HRs (95% CIs) ranged from 1.24 (95% CI, 1.23-1.26) in NHWs to 1.11 (95% CI, 1.07-1.15) in APIs among males and from 1.17 (95% CI, 1.15-1.18) in NHWs to 1.07 (95% CI, 1.04-1.11) in APIs among females. All-cause mortality associated with unmarried status compared with married status was higher in US-born API and Hispanic men and women relative to their foreign-born counterparts. CONCLUSIONS:For patients who have the cancers that contribute most to mortality, being unmarried is associated with worse overall survival compared with being married, with up to 24% higher mortality among NHW males but only 6% higher mortality among foreign-born Hispanic and API females. Future research should pursue the identification of factors underlying these associations to inform targeted interventions for unmarried cancer patients. Cancer 2016;122:1570-8. © 2016 American Cancer Society.