Infectious diseases such as HIV/AIDS, hepatitis C, and sexually transmitted diseases are more prevalent in prisoners than in the general population. In Western European prisons, inmates have HIV infection rates 25 times higher and hepatitis C infection rates 40 times higher than their national averages. To inform prisoners about the dangers of these diseases, a structured information exchange was ... [Show full abstract] developed. In a pre-/post- design with repeated measurement, 21 male prisoners' knowledge of infectious diseases was analyzed. A significant improvement of knowledge (p < .0001) was observed. One striking finding was that knowledge of hepatitis C was clearly lower than that of HIV and that prisoners enrolled in drug substitution programs were significantly better informed about hepatitis C than the other participating prisoners.