Increasing evidence link sleep curtailment and circadian misalignment with adverse metabolic outcome. Adolescents might be most affected, given their late sleep timing and early school and work start times.Our aim was to examine the impact of poor sleeping habits on glycemic control in adolescents with type 1 diabetes.This was a non-interventional multicenter study across Germany recruiting pubertally mature adolescents with type 1 diabetes. Medical records were used to collect information on diabetes duration, treatment, and complications. Participants self-reported sleep quality, timing, chronotype, and social jetlag—a measure of circadian misalignment. Hemoglobin A1c (HbA1c) was determined at the time of questionnaire response. We used multivariable linear regression models to examine associations between sleep and glycemic control.A total of 191 patients aged 16.5 years (mean HbA1c 8.0% [64 mmol/mol]) were included in this study. In multivariable adjusted analyses, sleep quality was significantly associated with HbA1c (mean difference; β = −0.07, P = .05). Stratified analysis indicated that this association might be stronger in boys and also in children with migration background. In contrast, neither sleep duration, sleep debt, chronotype, nor social jetlag was associated with HbA1c . Secondary analyses showed that social jetlag was significantly associated with levels of insulin requirements (mean difference; β = 0.035, P = .03).Our study suggests that poor sleep quality is associated with increased HbA1c in adolescents with type 1 diabetes and that higher levels of circadian misalignment are associated with increased insulin requirements. If replicated, our results indicate a clinical relevance of sleep habits in adolescents with type 1 diabetes.