Little is known about what factors affect the health-related quality of life (HRQoL) of adolescents and young adults (AYAs) with sickle cell disease (SCD), and how their HRQoL changes over time. This retrospective study included 87 AYAs attending a SCD Adolescent Clinic who completed a measure of HRQoL at each visit over the course of approximately 1.3 years. Results suggested that the following were associated with poorer physical HRQoL: being female, more healthcare utilization events, and presence of internalizing symptoms. Internalizing and externalizing symptoms were the only factors correlated with poorer psychosocial HRQoL. Generalized linear mixed models indicated that physical and psychosocial HRQoL improved among all participants during the assessment period, and those with externalizing behaviors reported faster improvement in physical HRQoL over time. AYAs with SCD may benefit from early mental health screening and intervention to optimize clinical care.