Despite the fact that more and more clinical case studies and research reports have been published on the increasing problem of Internet addiction, no generally accepted standardized tool is available to measure problematic Internet use or Internet addiction. The aim of our study was to create such a questionnaire. On the basis of earlier studies and our previous experience withYoung's (1998a) Internet Addiction Test, initially, we created a 30-item questionnaire, which was assessed together with other questions regarding participants' Internet use. Data were collected online from 1,037 persons (54.1% of them male; mean age, 23.3 years; SD, 9.1). As a result of reliability analysis and factor analysis, we reduced the number of items to 18 and created the Problematic Internet Use Questionnaire (PIUQ) containing three subscales: obsession, neglect, and control disorder. Cronbach's alpha of the PIUQ is .87 (Cronbach's alpha of the subscales is .85, .74, and .76, respectively). The test-retest correlation of the PIUQ is .90. The PIUQ proved to be a reliable measurement for assessing the extent of problems caused by the "misuse" of the Internet; however, further analysis is needed.