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OBJECTIVE—People with type 1 diabetes have increased risk of hospital admission compared with those without diabetes. We hypothesized that HbA1c would be an important indicator of risk of hospital admission. RESEARCH DESIGN AND METHODS—The Scottish Care Information–Diabetes Collaboration, a dynamic national register of diagnosed cases of diabetes in Scotland, was linked to national data on admissions. We identified 24,750 people with type 1 diabetes during January 2005 to December 2007. We assessed the relationship between deciles of mean HbA1c and hospital admissions in people with type 1 diabetes adjusting for patient characteristics. RESULTS—There were 3,229 hospital admissions. Of the admissions, 8.1 % of people had mean HbA1c,7.0 % (53 mmol/mol) and 16.3 % had HbA1c,7.5 % (58 mmol/mol). The lowest odds of admission were associated with HbA1c 7.7–8.7 % (61–72 mmol/mol). When compared with this decile, a J-shaped relationship existed between HbA1c and admission. The highest HbA1c decile (10.8–18.4%/95–178 mmol/mol) showed significantly higher odds ratio (95 % CI) for any admission (2.80, 2.51–3.12); the lowest HbA1c decile (4.4–7.1%/25–54 mmol/mol) showed an increase in odds of admission of 1.29 (1.10–1.51). The highest HbA1c decile expe