To investigate whether liraglutide added to treat-to-target insulin improves glycemic control and reduces insulin requirements and body weight in subjects with type 1 diabetes. A 52-week, double-blind, treat-to-target trial involving 1,398 adults randomized 3:1 to receive once-daily subcutaneous injections of liraglutide (1.8, 1.2, or 0.6 mg) or placebo added to insulin. HbA1c level was reduced 0.34-0.54% (3.7-5.9 mmol/mol) from a mean baseline of 8.2% (66 mmol/mol), and significantly more for liraglutide 1.8 and 1.2 mg compared with placebo (estimated treatment differences ETDs: 1.8 mg liraglutide -0.20% 95% CI -0.32; -0.07; 1.2 mg liraglutide -0.15% 95% CI -0.27; -0.03; 0.6 mg liraglutide -0.09% 95% CI -0.21; 0.03). Insulin doses were reduced by the addition of liraglutide 1.8 and 1.2 mg versus placebo (estimated treatment ratios: 1.8 mg liraglutide 0.92 95% CI 0.88; 0.96; 1.2 mg liraglutide 0.95 95% CI 0.91; 0.99; 0.6 mg liraglutide 1.00 95% CI 0.96; 1.04). Mean body weight was significantly reduced in all liraglutide groups compared with placebo ETDs (1.8 mg liraglutide -4.9 kg 95% CI -5.7; -4.2; 1.2 mg liraglutide -3.6 kg 95% CI -4.3; -2.8; 0.6 mg liraglutide -2.2 kg 95% CI -2.9; -1.5). The rate of symptomatic hypoglycemia increased in all liraglutide groups (estimated rate ratios: 1.8 mg liraglutide 1.31 95% CI 1.07; 1.59; 1.2 mg liraglutide 1.27 95% CI 1.03; 1.55; 0.6 mg liraglutide 1.17 95% CI 0.97; 1.43), and hyperglycemia with ketosis increased significantly for liraglutide 1.8 mg only (event rate ratio 2.22 95% CI 1.13; 4.34). Liraglutide added to insulin therapy reduced HbA1c levels, total insulin dose, and body weight in a population that was generally representative of subjects with type 1 diabetes, accompanied by increased rates of symptomatic hypoglycemia and hyperglycemia with ketosis, thereby limiting clinical use in this group.