Internet Addiction (IA) is discussed as a serious health problem. Epidemiologic investigations show prevalence rates of 3% of internet users that fulfil criteria for IA. Reported symptoms like tolerance, withdrawal, and craving resemble those of substance-related disorders. Although there is no final agreement on the classification of IA, it has often been referred to as a non-substance-related addiction fostering current issues on the next revision of DSM (Holden, 2010).

Although IA has been investigated in epidemiologic studies there is no research of its prevalence in patients in treatment because of a substance-related disorder. Regarding similarities between IA and substance-related disorders, theories suggest increased prevalence of comorbid IA in these patients.

This study focused on the identification of prevalence of comorbid IA among patients with a primary substance-related disorder in different in-patient clinics across Germany.

Sponsored by the German Federal Ministry of Health 1826 patients were screened with a diagnostic inventory for IA. For further description additional questionnaires were given assessing aspects of personality (NEO-FFI) and psychopathology (SCL-90R, BDI-II).

4.1% of the patients fulfilled criteria of IA. In these most common primary diagnoses were pathological gambling and dependency of cannabis. Concerning personality IA-subsample showed increased neuroticism and introversion. Highest symptom burden was found in depression and social insecurity.

Among patients with substance-related disorder prevalence of IA is more common than in healthy samples. Results recommend separate screening for IA in inpatient clinics for substance-related disorders to guarantee full psychological care for patients with IA.