Background: This study assessed the direction of the relationship between symptoms of insomnia disorder, depression, various anxiety disorders and obsessive compulsive disorder (OCD) in adolescents after controlling for age, gender, chronotype, and outcome variable at baseline. Methods: Data was collected in eight high schools in Adelaide, South Australia, at two time-points approximately 6 months apart. The study was completed by 318 and 255 high school students at baseline and follow-up, respectively, aged 12-18 (M=14.96, SD=1.34) in grades 7-11 at baseline. Hierarchical regression analyses were used to assess each relationship, the first model controlling for age, gender and chronotype, and the second controlling for outcome variable at baseline. Results: Insomnia symptoms predicted and were predicted by symptoms of each psychiatric disorder in model 1. In model 2, insomnia symptoms predicted symptoms of depression, and vice-versa. Symptoms of insomnia also predicted symptoms of separation anxiety disorder (SAD), but not vice-versa, in model 2. Symptoms of obsessive compulsive disorder (OCD) and social phobia (SP) predicted symptoms of insomnia disorder in model 2, but not vice-versa. Insomnia symptoms were no longer related to symptoms of other anxiety disorders in model 2. Limitations: The use of self-report measures, and potential predisposing, precipitating, perpetuating or preventative factors were not assessed. Conclusions: Symptoms of insomnia disorder are bidirectionally related to depressive symptoms independent from baseline symptoms, and unidirectionally related to symptoms of OCD and SP where OCD and SP are independent risk-factors of the development of insomnia symptoms.