BACKGROUND: Hypoglycemia is a major concern in older adults with type 1 diabetes (T1D) and there is limited knowledge in this population. We examined data from 199 adults, >/=60 years of age, who participated in a T1D Exchange study assessing factors associated with severe hypoglycemia (SH) in older adults with T1D: 100 with SH in the prior year and 99 with no SH in prior 3 years (mean age 68; mean diabetes duration 40 years; 47% female; 92% non-Hispanic white). Hypoglycemia was assessed with up to 14 days of blinded continuous glucose monitoring (CGM). Linear regression models were performed to assess the association between biochemical hypoglycemia [defined as percentage of time below specific cutoffs (<70/60/50 mg/dL)] and various factors. RESULTS: Overall, participants had CGM values <70 mg/dL for a median of 91 min per day. On 53% of days, glucose levels continuously were <70 mg/dL for >/=20 min. Hypoglycemia was found to be strongly associated with glucose variability (r = 0.76; P < 0.001). Time spent in hypoglycemia was greater in those who were younger (P = 0.004), had shorter diabetes duration (P = 0.008), lower HbA1c (P < 0.001), and undetectable C-peptide (P = 0.001), but did not differ by insulin method, education level, number of blood glucose checks per day, cognition, activities of daily living, or fear of hypoglycemia. INNOVATION: This study adds valuable data on the frequency of hypoglycemia in older adults with T1D. CONCLUSION: Future studies need to focus on how to prevent hypoglycemia in this vulnerable population of older adults with long-standing T1D.