Radiation is an important aspect of daily life. We interact with radiation from several sources, both natural and manmade, and in fact life on Earth depends on it. Although the general population, and students in particular, can recognize its importance, it is not clear whether they understand its meaning. Bearing these considerations in mind, a study of Portuguese students' knowledge of radiation physics was made and 1246 students from different school levels answered a questionnaire on the subject. In this work we report some of the results obtained.