BACKGROUND : As children with diabetes transition to adulthood, they may be especially vulnerable to diabetic ketoacidosis (DKA). Cross-national comparisons may inform efforts to avoid this complication. OBJECTIVE : To compare DKA hospitalization rates in the USA and Manitoba, Canada, during the vulnerable years known as "emerging adulthood." METHODS : Cross-sectional study using inpatient administrative databases in the USA (years 1998-2014) and Manitoba, Canada (years 2003-2013). METHODS : Individuals aged 12-30 years hospitalized with DKA, identified using ICD-9 (USA) or ICD-10 codes (Manitoba). METHODS : DKA hospitalization rates per 10,000 population by age (with a focus on those aged 15-17 vs. 19-21). Admissions were characterized by gender, socioeconomic status, year of hospitalization, and mortality during hospitalization. RESULTS : The DKA rate was slightly higher in the USA among those aged 15-17: 4.8 hospitalizations/10,000 population vs. 3.7/10,000 in Manitoba. Among those aged 19-21, the DKA hospitalization rate rose 90% in the USA to 9.2/10,000, vs. 23% in Manitoba, to 4.5/10,000. In both the USA and Manitoba, rates were higher among those from poorer areas, and among adolescent girls compared with adolescent boys. DKA admissions rose gradually during the period under study in the USA, but not in Manitoba. CONCLUSIONS : In years of "emerging adulthood," the Canadian healthcare system appears to perform better than that of the USA in preventing hospitalizations for DKA. Although many factors likely contribute to this difference, universal and seamless coverage over the lifespan in Canada may contribute.