The spontaneous reporting system (srs) is the most important early warning system of adverse drug reactions. As there is serious under-reporting we studied the respective knowledge and attitudes of two samples of physicians in Germany. Five hundred randomly sampled physicians and 815 physicians who had actually reported an ADR were included; the response rate to the mail questionnaire was 51.4 and 43.9%, respectively; 61.3% said to have reported at least one case in their life. As many as 75–85% of physicians said never to have sent an ADR report to the governmental or professional reporting systems. Reporting to pharmaceutical companies, on the other hand, has been substantially better. Sixty-eight and two-tenths percent indicated to have suspected an ADR without reporting it. Major reasons for not reporting were: ADR well known (75.6%), too trivial (71.1%), causality uncertain (66.3%). The ADR with the highest probability of being reported were serious unknown adverse reactions of a new drug (81.1%) or an established drug (72.9%) and serious known reactions to a new drug (65.2%). Almost 20% of the physicians admitted to not know the spontaneous reporting system and 30% to not know how to report; 54% would rather report an ADR if therapeutic advice was offered. The results indicate that the traditional ways of advertising the srs and communicating with physicians could be improved. Proactive services and professional marketing of srs are needed to reduce underreporting.