Insomnia is prevalent in adolescents. Impulsive behaviours and excessive risk-taking have been linked to the manifestation of psychopathology in youths. Previous research based on behavioural and neurophysiological measures has found that individuals with insomnia demonstrated impaired inhibitory control, which is associated with detrimental outcomes such as substance abuse and self-harm. Existing evidence has shown some positive effects of cognitive behavioural therapy for insomnia (CBT-I) on insomnia symptoms and daytime functioning in youths. Given the link between insomnia and impulsivity reported in previous research, and sleep as a highly modifiable factor, we are conducting this randomised controlled trial to examine the impact of CBT-I in improving impulsivity and risk-taking in youth with insomnia.