This study aims at determining the extent to which computer using skills specified in Project for International Students Evaluation (PISA) 2006 predict Turkish students' achievement in mathematics. Apart from questions on mathematics, science and reading competencies, a student questionnaire, a school questionnaire and a parent questionnaire were also given prior to the exam to gather information on various social, cultural and economic factors that might be related to the students' academic achievement. Self-reliance in performing the operations requiring high level of computer skills, self-reliance in performing internet-related operations, using computers for internet and entertainment purposes, and using computers for programme and software purposes were examined as variables affecting mathematical achievement in this research. Multiple regression analysis was conducted so as to determine the degree to which independent variables predicted achievement at mathematics. The analysis results showed that the model constructed was statistically significant (F = 240.45; p less than 0.01). The independent variables accounted for approximately 17.7% of the overall variance. The research findings showed that students' self-reliance in performing the operations requiring high level of computer skills, using the word processor, using electronic tabulating programme in drawing graphs, preparing presentations, preparing multi-media presentations, and designing web pages affected the mathematics achievement scores in a negative way. Based on those results, it might be said that students' using computers in line with their needs, parents' controlling the time their children use computers, the internet and computer for entertainment purposes would be beneficial. (Contains 3 tables.)