This study investigated the relationships between subjective and objective sleep outcomes and lifestyle factors (i.e., nap duration, screentime, chronotype, use of tobacco, alcohol, caffeine, and medications) in young adults who sustained traumatic brain injury (TBI) in childhood. The study was conducted at the Murdoch Children&rsquo;s Research Institute and Royal Children&rsquo;s Hospital (Australia). It reports cross-sectional data collected at 20 years post-childhood TBI, as part of a prospective study. Participants included 54 young adults with TBI (mean age, 27.7; standard deviation [SD], 3.2 years) who were assessed at 20 years post-injury (mild [n = 14], moderate [n = 27], and severe [n = 13] TBI) and 13 healthy controls (mean age, 26.0; SD, 2.1 years). Sleep was assessed with the Pittsburgh Sleep Quality Index and actigraphy, and lifestyle factors were assessed with a study-designed questionnaire. Objective sleep efficiency was not significantly different between the TBI and control groups, but the control group presented with significantly better subjective sleep quality compared to the mild and moderate TBI severity groups. Poor subjective sleep quality was significantly associated with evening chronotype (P < 0.001) and tobacco use (P < 0.001), while being a parent (P = 0.038) and alcohol use (P = 0.035) were significantly associated with poorer objective sleep efficiency in the TBI group. These preliminary findings highlight interesting associations between poor sleep quality and lifestyle factors in young adults who sustained TBI in childhood. They highlight the need to further explore these relationships in this TBI population to inform on potential avenues for sleep interventions.