BACKGROUND Anthelmintics are commonly used in tropical areas, but are also prescribed in Western countries with other climates. However, pharmacoepidemiologic studies of these drugs are rare. OBJECTIVE To investigate adverse drug reactions (ADRs) due to anthelmintics. METHODS All spontaneous reports of ADRs associated with albendazole, diethylcarbamazine, flubendazole, ivermectin, mebendazole, niclosamide, praziquantel, pyrantel pamoate, and thiabendazole were identified in the French Pharmacovigilance Database from January 1, 1985, to August 31, 1999. For each case, the following data were recorded: age, gender, weight, ADRs, drug, dosage, and indication. RESULTS A total of 243 cases were found corresponding to 291 ADRs. Serious ADRs (hematologic or hepatic injury) to albendazole most often occurred when the drug was used for the treatment of echinococcosis or cysticercosis, thus requiring both high dosage and long duration of therapy. Our data show that the profile and seriousness of anthelmintic-induced ADRs vary according to their use. Furthermore, the low number of spontaneous reporting of ADRs suggests a high rate of underreporting for these drugs, which are often considered in France as orphan drugs. CONCLUSIONS The improvement of reporting of serious or unrecognized (unlabeled) anthelmintic-induced ADRs will increase our knowledge of the benefit/risk ratio associated with these agents and optimize their use.