Helminth infections are now recognised as being a major health priority worldwide. Morbidity due to these infections can be controlled at a reasonable cost by means of periodic chemotherapy using effective drugs. Deworming campaigns targeted at high risk groups, such as school-age children, pre-school children and women of child-bearing age, are the mainstay of the control strategy launched by WHO. Anthelminthic drugs can be delivered effectively through the school system, women's associations or other community-based interventions, each of which often lack health personnel supervision. The safety of anthelminthic drugs is, therefore, of paramount importance and side effects have to be recognised and monitored, especially when generic drugs are widespread. Four anthelminthic drugs are considered to provide appropriate single dose treatment against soil-transmitted helminthiasis: albendazole, levamisole, mebendazole and pyrantel. Side effects, at the dosage recommended for deworming, have been described as negligible and self-limiting. However, a limited number of reports have associated more severe adverse reactions to the distribution of anthelminthic medicines. Even if the available information cannot confirm a cause-effect relationship, it is essential that these effects are known. Ministries of Health can then set up efficient and safe delivery, monitoring and referral systems, in order to minimise the risk and maximise the benefit of periodic anthelminthic chemotherapy in communities where soil-transmitted helminthiasis is endemic.