Attention deficit hyperactivity disorder (ADHD) is a common neurobehavioural disorder which has been associated with sleep and circadian rhythm disturbances. Numerous studies have linked evening circadian typology with traits and behaviours associated with the disorder, although a precise reason for this relationship has not been clarified. The current study examines ADHD symptoms, impulsivity, cognitive failures, sleep quality and chronotype in a cohort of healthy young adults (N = 396). Results show significant, small magnitude associations between mid-point of sleep on free days, social jetlag (SJL) and ADHD symptoms and impulsivity, although not with cognitive failures. Similarly, sleep quality is also associated with ADHD symptoms and impulsivity. Group-wise approaches show that higher SJL is associated with significantly more ADHD symptoms and impulsivity, and later mid-sleep on free days is also associated with more ADHD symptoms. Stepwise multiple linear regression reveals that, when controlling for age and sex, SJL but not mid-sleep on free days is a significant predictor of ADHD symptoms and impulsivity. These results indicate that SJL may be an important factor to consider when exploring circadian rhythm associations with ADHD symptoms.