The co-occurrence of insomnia and mental disorders constitutes the most prevalent diagnosis pattern found in sleep disorder clinics. Yet, there remains a paucity of epidemiological information regarding comorbidity of mental disorders and sleep disorder symptomatology in the general population. The present study showed results based on a large representative French cohort (n = 5,622; 80.7% of the contacted stratified sample). A total of 997 (17.7%) individuals with insomnia complaints were identified and divided into six diagnostic categories: (1) Insomnia related to a Depressive Disorder; (2) Insomnia related to an Anxiety Disorder; (3) Depressive Disorder accompanied by insomnia symptomatology; (4) Anxiety Disorder accompanied by insomnia symptomatology; (5) Primary Insomnia; and (6) isolated insomnia symptomatology. Telephone interviews were conducted using the Sleep-Eval System. Subjects with insomnia related to a Mental Disorder have a longer history of insomnia complaints and are usually younger than those with Depressive or Anxiety Disorders accompanied by insomnia symptoms. Subjects with Insomnia related to a Depressive Disorder experienced more repercussions than any other group. A surprisingly high percentage of individuals with depressive symptomatology had sought independent medical treatment specifically for their sleep problems, which raises the unsettling possibility that many cases of depression go undetected by the general medical community. The distinct predictability of commonly undiagnosed depression leading to chronic depression speaks directly to the imperative that physicians receive additional training in this area of community mental health.