The objective of this research was to assess the predictive power of various Internet applications on the development of compulsive Internet use (CIU). The study has a two-wave longitudinal design with an interval of 1 year. The first measurement contained 447 adult heavy Internet users who used the Internet at least 16 h per week and had Internet access at home for at least 1 year. For the second measurement, all participants were invited again, of whom 229 responded. By means of an online questionnaire, the respondents were asked about the time spent on various Internet applications and CIU. On a cross-sectional basis, gaming and erotica seem the most important Internet applications related to CIU. On a longitudinal basis, spending a lot of time on erotica predicted an increase in CIU 1 year later. The addictive potential of the different applications varies; erotica appears to have the highest potential.