In 2009, we can look back on a history of 40 years of internet use. While most consumers make use of the internet in a controlled fashion, a progressive loss of the ability to control the frequency and duration of internet activities emerges in some users. As a consequence, the excessive time devoted to internet use and the behavioural narrowing can lead to dramatic psychosocial outcomes. This phenomenon is referred to as "pathological internet use" (PIU). On behalf of the German ministry of health a systematic review of the literature since 1996 has been carried out. The main results will be presented in this review. Prevalence data on pathological internet use are limited by methodological difficulties concerning the diagnosis and the heterogeneity of diagnostical instruments. International prevalence rates range from 1.5 % to 8.2 %. Annual studies on representative samples of the German population describe their internet use and patterns of use, but information on the prevalence of PIU is missing. Diagnostical instruments are needed that show sufficient reliability and validity and allow international comparisons. Research on the Dutch "Compulsive Internet Use Scale" may close this gap. Cross-sectional studies on samples of patients report high comorbidity of PIU with psychiatric disorders, e. g. affective disorder and attention deficit hyperactivity disorder (ADHD). If PIU and these co-occurring disorders could be explained by shared risk factors or better as secondary disorders is largely unknown. The treatment currently is based on therapeutical interventions and strategies successful in the treatment of substance use disorders. Due to the lack of methodological sufficient research it is currently impossible to recommend any evidence-based treatment of PIU.
