OBJECTIVE: To compare the 12-month effects of continuous glucose monitoring (CGM) versus blood glucose monitoring (BGM) in adults with insulin-treated type 2 diabetes. RESEARCH DESIGN AND METHODS: This is a single-center, parallel, open-label, randomized controlled trial including adults with inadequately controlled, insulin-treated type 2 diabetes from the outpatient clinic at Steno Diabetes Center Copenhagen, Denmark. Inclusion criteria were ≥18 years of age, insulin-treated type 2 diabetes, and HbA1c ≥7.5% (58 mmol/mol). Participants were randomly assigned (1:1) to 12 months of either CGM or BGM. All participants received a diabetes self-management education course and were followed by their usual health care providers. Primary outcome was between-group differences in change in time in range (TIR) 3.9-10.0 mmol/L, assessed at baseline, after 6 and 12 months by blinded CGM. The prespecified secondary outcomes were differences in change in several other glycemic, metabolic, and participant-reported outcomes. RESULTS: The 76 participants had a median baseline HbA1c of 8.3 (7.8, 9.1)% (67 [62-76] mmol/mol), and 61.8% were male. Compared with BGM, CGM usage was associated with significantly greater improvements in TIR (between-group difference 15.2%, 95% CI 4.6; 25.9), HbA1c (-0.9%, -1.4; -0.3 [-9.4 mmol/mol, -15.2; -3.5]), total daily insulin dose (-10.6 units/day, -19.9; -1.3), weight (-3.3 kg, -5.5; -1.1), and BMI (-1.1 kg/m2, -1.8; -0.3) and greater self-rated diabetes-related health, well-being, satisfaction, and health behavior. CONCLUSIONS: In adults with inadequately controlled insulin-treated type 2 diabetes, the 12-month impact of CGM was superior to BGM in improving glucose control and other crucial health parameters. The findings support the use of CGM in the insulin-treated subgroup of type 2 diabetes.