Context: Glycemic targets and the benefit of intensive glucose control are currently under debate as intensive glycemic control has been suggested to have negative effects on mortality risk in type 2 diabetes patients. Objective: We examined the association between glycated hemoglobin (HbA1c) and all-cause mortality in patients with type 1 diabetes mellitus. Design, Setting, and Patients: A clinic-based prospective cohort study was performed in 2,764 European patients with type 1 diabetes aged 15-60 years enrolled in the EURODIAB Prospective Complications Study. Outcome measure: Possible non-linearity of the association between HbA1c and all-cause mortality was examined using multivariable restricted cubic spline regression using three (at HbA1c 5.6, 7.1, 8.1, 9.5 and 11.8%) and five knots (additionally at HbA1c 7.1 and 9.5%). Mortality data were collected ~7 years after baseline examination. Results: HbA1c was related to all-cause mortality in a non-linear manner after adjustment for age and sex. All-cause mortality risk was increased at both low (5.6%) and high (11.8%) HbA1c compared to the reference (median HbA1c: 8.1%) following a U-shaped association (P overall effect=0.008 and 0.04, P non-linearity=0.03 and 0.11 (three and five knots, respectively)). Conclusions: Results from our study in type 1 diabetes patients suggest that target HbA1c below a certain threshold may not be appropriate in this population. We recognize that these low HbA1c levels may be related to anemia, renal insufficiency, infection, or other factors not available in our database. If our data are confirmed, the potential mechanisms underlying this increased mortality risk among those with low HbA1c will need further study.