Sleep behavior is changing toward shorter sleep duration and later chronotype. It results in a sleep debt that is acquitted on work-free days, inducing a small but recurrent sleep misalignment each week, referred to as "social jetlag". These sleep habits could affect health through misalignment with circadian rhythms.To address the impact of sleep behavior on glycemic control, assessed by HbA1c, in patients with type 1 diabetes, independently of other lifestyle or sleep-related factors.to address whether circadian phase impacts glycemic control.Eighty adult patients with type 1 diabetes (46% female) were included in a clinical cohort study.Sleep behavior was addressed objectively by a 7-days actimetry, lifestyle by questionnaires, sleep breathing disorders by nocturnal oximetry and circadian phase by dim light melatonin onset (DLMO).Univariate analyses showed that chronotype (r=0.23, p=0.042) and social jetlag (r=0.30, p=0.008) were significantly associated with HbA1c. In multivariable analysis, social jetlag was the only sleep habit independently associated with HbA1c (β=0.012 (0.006; 0.017), p<0.001). HbA1c was lower in patients with a social jetlag below vs. above the median (7.7% [7.1-8.7] and 8.7% [7.6-9.8], p=0.011). DLMO was not associated with HbA1c. However, the later the DLMO the worse the sleep efficiency (r=-0.41, p<0.001) and fragmentation index (r=0.35, p=0.005).Social jetlag, a small but recurrent circadian misalignment, is associated with worse glycemic control in type 1 diabetes whereas circadian phase is not. Further intervention studies should address the potential improvement of glycemic control by correcting social jetlag.