OBJECTIVE To examine the magnitude and types of hospitalizations among persons with prediabetes, undiagnosed diabetes, and diagnosed diabetes. RESEARCH DESIGN AND METHODS This study included 13,522 participants in the Atherosclerosis Risk in Communities (ARIC) study (mean age 57 years, 56% female, 24% black, 18% with prediabetes, 4% with undiagnosed diabetes, 9% with diagnosed diabetes) with follow-up in 1990–2011 for hospitalizations. Participants were categorized by diabetes/HbA1c status: without diagnosed diabetes, HbA1c <5.7% (reference); prediabetes, 5.7 to <6.5%; undiagnosed diabetes, ≥6.5%; and diagnosed diabetes, <7.0 and ≥7.0%. RESULTS Demographic adjusted rates per 1,000 person-years of all-cause hospitalizations were higher with increasing diabetes/HbA1c category (Ptrend < 0.001). Persons with diagnosed diabetes and HbA1c ≥7.0% had the highest rates of hospitalization (3.1 times higher than those without a history of diagnosed diabetes, HbA1c <5.7%, and 1.5 times higher than those with diagnosed diabetes, HbA1c <7.0%, P < 0.001 for both comparisons). Persons with undiagnosed diabetes had 1.6 times higher rates of hospitalization and those with prediabetes had 1.3 times higher rates of hospitalization than those without diabetes and HbA1c <5.7% (P < 0.001 for both comparisons). Rates of hospitalization by diabetes/HbA1c category were different by race (Pinteraction = 0.011) and by sex (Pinteraction = 0.020). There were significantly excess rates of hospitalizations due to cardiovascular, endocrine, respiratory, gastrointestinal, iatrogenic/injury, neoplasm, genitourinary, neurologic, and infection causes among those with diagnosed diabetes compared with those without a history of diagnosed diabetes (all P < 0.05). CONCLUSIONS Persons with diagnosed diabetes, undiagnosed diabetes, and prediabetes are at a significantly elevated risk of hospitalization compared with those without diabetes. Substantial excess rates of hospitalizations in persons with diagnosed diabetes were for endocrine, infection, and iatrogenic/injury causes, which may be preventable with improved diabetes care.