Background and Purpose— Sulfonylureas block nonselective cation channels and lower serum glucose and are neuroprotective in animal models of ischemic stroke. Human data on sulfonylureas in acute stroke are sparse and conflicting. We aimed to measure the potential neuroprotective effect of prestroke sulfonylurea use in diabetic patients. Methods— We analyzed data from a prospective cohort of individuals with diabetes mellitus (DM) enrolled in nonreperfusion ischemic stroke trials within Virtual International Stroke Trials Archive (VISTA) comprising 1050 patients, 298 with sulfonylurea use before stroke onset. The primary outcome measures were baseline National Institutes of Health Stroke Scale score and 90-day modified Rankin Scale score. Results— Compared with patients on no DM medications, those with sulfonylurea use before stroke onset presented with less severe stroke (OR, 0.69; 95% CI, 0.53 to 0.89) but had similar modified Rankin Scale scores at 90 days (OR, 0.95; 95% CI, 0.74 to 1.23). Compared with those on other DM agents, there was no difference in initial stroke severity (OR, 1.04; 95% CI, 0.73 to 1.48) nor modified Rankin Scale score at 90 days (OR, 1.00; 95% CI, 0.71 to 1.40). Compared with those using any DM medication, patients not on any treatment experienced higher initial National Institutes of Health Stroke Scale scores (OR, 1.48; 95% CI, 1.18 to 1.86) and were marginally more likely to have poor outcomes (modified Rankin Scale score >2) at 90 days (OR, 1.31; 95% CI, 0.97 to 1.77). Conclusions— Sulfonylurea use before stroke onset did not affect stroke severity or long-term functional outcome compared with other DM treatments. This finding casts doubt on the use of sulfonylureas for prophylactic neuroprotection. Furthermore, patients not using any medication for DM appear to have more severe strokes and worse outcomes.