To examine whether neighborhood socioeconomic status (SES) is a predictor of non-drug-related health care costs among Canadian adults with diabetes and, if so, whether SES disparities in costs are reduced after age 65 years, when universal drug coverage commences as an insurable benefit.Administrative health databases were used to examine publicly funded health care expenditures among 698,113 younger (20-64 years) and older (≥65 years) adults with diabetes in Ontario from April 2004 to March 2014. Generalized linear models were constructed to examine relative and absolute differences in health care costs (total and non-drug-related costs) across neighborhood SES quintiles, by age, with adjustment for differences in age, sex, diabetes duration, and comorbidity.Unadjusted costs per person-year in the lowest (Q1) versus highest (Q5) SES quintile were 39% higher among younger adults ($5,954 vs. $4,270 [Canadian dollars]) but only 9% higher among older adults ($10,917 vs. $9,993). Adjusted nondrug costs (primarily for hospitalizations and physician visits) were $1,569 per person-year higher among younger adults in quartile (Q)1 vs. Q5 (modeled relative cost difference: 35.7% higher) and $139.3 million per year among all individuals in Q1. Scenarios in which these excess costs per person-year were decreased by ≥10% or matched the relative difference among seniors suggested a potential for savings in the range of $26.0-$128.2 million per year among all lower-SES adults under age 65 years (Q1-Q4).SES is a predictor of diabetes-related health care costs in our setting, more so among adults under age 65 years, a group that lacks universal drug coverage under Ontario's health care system. Non-drug-related health care costs were more than one-third higher in younger, low-SES adults, translating to >$1 billion more in health care expenditures over 10 years.