The Generalized Pathological Internet Use Scale (GPIUS2) assesses cognitive behavioral aspects of problematic Internet use. To date, the 15-item scale has only been available in English, and the aim of this study was to translate and validate a German version. An online sample (ON, n = 1,041, age 24.2 +/- 7.2 years, 46.7% men) completed an Internet version of the translated GPIUS2, and a student sample (OF, n = 841, age 23.5 +/- 3.0 years, 46.8% men) filled in a pencil and paper version. A third sample of 108 students (21.5 +/- 2.0 years, 25.7% men) completed the questionnaire twice to determine the 14-day retest reliability. Participants also answered questions regarding their Internet use habits (OF, ON) and depression, loneliness, and social anxiety (ON). The internal consistencies were alpha = 0.91 (ON) and alpha = 0.86 (OF). Item-whole correlations ranged from r = 0.53 to r = 0.69 (ON) and from r = 0.39 to r = 0.63 (OF). The 2 week retest reliability was r(tt) = 0.85. Confirmatory factor analyses found a satisfactory fit for the factorial model proposed by Caplan for the original version. The GPIUS2 score correlated moderately with time spent on the Internet for private purposes in a typical week (ON: r = 0.40; OF: r = 0.36). Loneliness, depression, and social anxiety explained 46% of the variance in GPIUS2 scores. The German version of the GPIUS2 has good psychometric properties in a pencil and paper version as well as in a web-based format, and the observations regarding loneliness, depression, and social anxiety support the underlying model.