ObjectiveTo assess real-world safety and effectiveness of dapagliflozin in people living with type 1 diabetes mellitus (T1DM). MethodsWe conducted a multicenter retrospective study in Spain including data from 250 people living with T1DM receiving dapagliflozin as add-on therapy to insulin (80.8 % on-label use). The number of diabetic ketoacidosis (DKA) events was calculated over a 12-month follow-up (primary outcome). Changes in body weight, HbA1c, total daily insulin dose, and continuous glucose monitoring (CGM) metrics from baseline (at dapagliflozin prescription) to 12 months were also evaluated. ResultsA total of five DKA events (2.4 % [95 % CI 0.3;4.5] were reported in patients with a 12-month follow-up, n = 207): two events related to insulin pump malfunction, two events related to concomitant illnesses, and one event related to insulin dose omission. DKA events were more frequent among insulin pump users than among participants on multiple daily injections (7.7 % versus 1.2 %). Four of the reported DKA events occurred within the first six months after initiation of dapagliflozin. No deaths or persistent sequelae due to DKA were reported. No severe hypoglycemia episodes were reported. Significant reductions in mean body weight (−3.3 kg), HbA1c (−0.6 %), and total daily insulin dose (−8.6 %), P < 0.001, were observed 12 months after dapagliflozin prescription. Significant improvements in TIR (+9.3 %), TAR (−7.2 %), TBR (−2.5 %), and coefficient of variation (−5.1 %), P < 0.001, were also observed in the subgroup of patients with available CGM data. Finally, an improvement in urinary albumin-to-creatinine ratio (UACR) was found among participants with UACR ≥ 30 mg/g at baseline (median decrease of 99 mg/g in UACR, P = 0.001). ConclusionThe use of dapagliflozin in people living with T1DM has an appropriate safety profile after careful selection of participants and implementation of strategies to reduce the risk of DKA (i.e., prescribed according to the recommendations of the European Medicines Agency), and also leads to clinical improvements in this population.