ABSTRACTThe aim of the study is to evaluate whether exercise interventions are associated with improved glycaemic control in children and adolescents with type 1 diabetes mellitus (T1DM), and to examine its relationship with the characteristics of the intervention (i.e. type, intensity, length, and duration of the sessions). Eligible criteria were randomised controlled trials of youth aged 6–18 years with T1DM, participating in an exercise‐based intervention where glycaemic control is measured (i.e. glycated haemoglobin [HbA1c]). Pooled effect sizes (Hedges'g) were calculated using random‐effects inverse‐variance analyses. Fourteen studies enrolling 509 patients were analysed. Effect size was expressed as Hedges’ g to correct for possible small sample bias. Overall, HbA1c levels in the exercise group (g = –0.38 95% confidence interval [CI], –0.66 to –0.11; mean difference [MD] = –0.62%) were reduced compared with the control group. Concurrent training (g = –0.63 95%CI, –1.05 to –0.21), high‐intensity exercise (g = –0.43 95%CI, –0.83 to –0.03), interventions ≥24 weeks (g = –0.92 95%CI, –1.44 to –0.40), and sessions ≥60 minutes (g = –0.71 95%CI, –1.05 to –0.08) showed larger changes (MD = –0.66% to 1.30%). In conclusion, our study suggests that programmes longer than 24 weeks with at least 60 min/session of high‐intensity concurrent exercise may serve as a supportive therapy to metabolic control in youth with T1DM.Highlights Exercise training has a moderate effect on the reduction of glycated haemoglobin (HbA1c) and insulin dose per day in youths with type 1 diabetes. Exercise training moderately increases cardiorespiratory fitness youths with type 1 diabetes. Reductions in HbA1c are stronger with high‐intensity and concurrent training (i.e. aerobic and strength) interventions, and longer programmes.