This paper analyzes anonymous political participation in the form of e-petition signing. The purpose of this study is to increase knowledge about patterns behind anonymous e-petition signing. Since online political participation evokes an important discussion about the balance between the need for transparency on the one hand, and the right for anonymity on the other hand, it is crucial to increase our knowledge of the factors affecting citizens’ choices to remain anonymous. Using quantitative content analysis of 220 informal e-petitions on the site adressit.com in Finland, this study seeks to find possible determinants for the share of anonymous signatures. Findings indicate that the type of demand presented in the e-petition is a key factor predicting the share of anonymous signatures.