Sleep duration and quality have been associated with many health outcomes, including weight management. We aimed to investigate the effect of self-reported sleep duration and quality on weight loss maintenance in participants of the MedWeight study, a registry of individuals that lost at least 10% of body weight in the past and either maintained the loss (maintainers: weight maintenance of at least 10% of initial weight loss) or regained it (regainers: weight ≥95% of their maximum body weight). Study participants included 528 volunteers (61% women). Sleep quantity referred to the reported duration of nocturnal sleep, as well as the frequency of mid-day naps during the last month. Sleep quality was assessed through the Athens Insomnia Scale (AIS). Reported sleep quantity was associated with weight maintenance status, but the association became non-significant when the AIS score entered the model. In specific, AIS was inversely associated with the likelihood of being a maintainer (OR=0.89 per AIS unit, 95% CI: 0.81 - 0.98), even after adjusting for potential confounders. Sex-specific analysis revealed that the association between the AIS score and maintenance status was evident in men but not in women. Future studies are needed to confirm these results in other population groups and reveal underlying mechanisms.