Objectives: Sleep disturbance and psychopathology are common during adolescence and are highly prevalent in individuals diagnosed with autism spectrum disorder (ASD). The aim of this study was to investigate relationships between sleep disturbance, psychopathology symptoms, and daytime functioning in adolescents with high-functioning autism spectrum disorder (HFASD) compared to typically developing (TD) adolescents. Methods: Twenty-seven adolescents with HFASD and 27 age- and sex-matched TD adolescents completed questionnaires related to sleep, psychopathology and daytime functioning. Participants also completed a 7-day sleep/wake diary. A subsample of HFASD adolescents (55%) and all the TD adolescents wore an actigraphy monitor concurrently with the sleep diary. Results: Adolescents with HFASD had significantly higher scores for depressed mood, anxiety and pre-sleep arousal compared with TD adolescents and poorer daytime functioning. There were more significant correlations between sleep variables and psychopathology variables, and sleep variables and daytime functioning, in the HFASD group than in the TD group. Standard regression found that sleep variables significantly accounted for 57% of the variance in daytime functioning symptoms of insufficient sleep in the HFASD group, while psychopathology variables accounted for 63% of the variance in daytime functioning. Conclusions: Both sleep disturbance and psychopathology are more prevalent in adolescents with HFASD and are major contributors to poor daytime functioning in these individuals.