To determine whether severe hypoglycemic and hyperglycemic events are associated with longitudinal dementia risk in older adults with type 1 diabetes. A longitudinal cohort study followed 2,821 members of an integrated healthcare delivery system with type 1 diabetes from 1997-2015. Hypoglycemic and hyperglycemic events requiring emergency room or hospitalization were abstracted from medical records beginning 1/1/1996 through cohort entry. Participants were followed for dementia diagnosis through 9/30/2015. Dementia risk was examined using Cox proportional hazard models adjusted for age (as timescale), sex, race/ethnicity, HbA1c, depression, stroke, and nephropathy. Among 2,821 older adults (mean age 56) with type 1 diabetes, 398 (14%) had a history of severe hypoglycemia, 335 (12%) severe hyperglycemia and 87 (3%) both. Over a mean 6.9 years of follow-up, 153 individuals (5.4%) developed dementia. In fully adjusted models, individuals with hypoglycemic events had 66% greater risk of dementia than those without a hypoglycemic event (HR=1.66; 95% CI: 1.09, 2.53), while those with hyperglycemic events had >2 times the risk (HR=2.11; 95% CI: 1.24, 3.59) than those without a hyperglycemic event. There was a 6-fold greater risk of dementia in individuals with both severe hypoglycemia and hyperglycemia versus those with neither (HR=6.20; 95% CI: 3.02, 12.70). For older individuals with type 1 diabetes, severe hypoglycemic and hyperglycemic events are associated with increased future risk of dementia.