Introduction: The paper presents original research designed to explore and compare selected aspects of the information seeking behaviour of mathematicians (scientists and students) on the Internet. Method: The data were gathered through a questionnaire distributed at the end of 2011 and in January 2012. Twenty-nine professional mathematicians and 153 students of mathematics from the Institute of Mathematics of the Jagiellonian University in Kraków, Poland, were surveyed. Analysis. The gathered data were analysed in a quantitative manner and then interpreted comparatively to find similarities and differences between the behaviour of professional mathematicians and students. Results: Students, as opposed to scientists, often declared searching for reference works and multimedia objects and comparatively rarely for journal papers and information about sources unavailable on the Web. They more willingly use social networking sites while scientists more often search discipline-oriented portals or library Websites. Scientists use, first of all, the author's name or the publication titles to formulate queries, students prefer keyword searching. While scientists trust their own ability to determine the scientific character of information or treat journals as determinants of the scientific quality, students do not. Conclusions: The research revealed some significant differences between the information seeking behaviour of those two groups of mathematicians. It could be the result of different levels of experience in scientific work, distinct tasks undertaken within the academic environment, and the change in the general paradigm of information searching.