Mozzillo E, et al. - The relationship between unhealthy lifestyle habits and health-related quality of life (HRQoL) in adolescents and young adults with type 1 diabetes mellitus (T1DM) was evaluated. In adolescents and young adults with T1DM, the clustering of unhealthy lifestyle habits was correlated with reduced HRQoL. To improve the health status and the HRQoL, promoting multiple behavior changes could be a useful approach in youths with T1DM.