OBJECTIVE Sulfonylureas are first-line treatment of hepatocyte nuclear factor 1-alpha (HNF1A) diabetes (maturity-onset diabetes of the young type 3), but many patients do not achieve optimal glycemic control without episodes of hypoglycemia. We investigated the combination of the sulfonylurea glimepiride and the dipeptidyl peptidase 4 inhibitor linagliptin versus glimepiride monotherapy with respect to glycemic variability, glycemic control, and risk of hypoglycemia. RESEARCH DESIGN AND METHODS In a randomized, double-blinded, crossover trial, patients with HNF1A diabetes (n= 19; mean +/- SD age 43 +/- 14 years, BMI 24.8 +/- 2.8 kg/m(2), and glycated hemoglobin [HbA(1c)] 7.4 +/- 0.2% [57.1 +/- 7.3 mmol/mol]) were randomly assigned to treatment with glimepiride + linagliptin 5 mg (16 weeks), washout (4 weeks), and glimepiride + placebo (16 weeks) (or vice versa). Glimepiride was titrated targeting a fasting plasma glucose of 4.5-6.0 mmol/L without hypoglycemia. Treatments were evaluated by continuous glucose monitoring (CGM), HbA(1c), and meal test. RESULTS Compared with glimepiride + placebo, glimepiride + linagliptin did not significantly improve the primary end point, mean amplitude of glycemic excursions (MAGE) (mean difference -0.7 mmol/L,P =0.1540), but displayed significant reductions in coefficient of variation on CGM (-3.6%,P =0.0401), HbA(1c)(-0.5%,P =0.0048), and glimepiride dose (-0.7 mg/day,P =0.0099). beta-cell glucose sensitivity (assessed as C-peptide-to-glucose ratio) during meal test improved with glimepiride + linagliptin. Incidences of hypoglycemia were similar with both treatments. CONCLUSIONS Linagliptin as add-on treatment to glimepiride improved glycemic variability and control without increasing risk of hypoglycemia in patients with HNF1A diabetes.