Insomnia is often comorbid with psychiatric, medical, and neurologic disorders. For years, insomnia was thought to be secondary to various disorders; therefore, it did not receive the attention it needed because the other disorder was viewed as playing the primary role in the insomnia problem. However, our thinking has moved away from treating the other condition to resolve the insomnia toward treating insomnia as a separate condition. Insomnia and comorbid conditions have a bidirectional effect, with the status of each impacting the other, potentially affecting the treatment course and outcome. This report describes conditions that commonly appear in patients with insomnia.