Data concerning lactrodectism in Madagascar is scarce. Two spider species of the Latrodectus genus are found on the Grand Isle: the black widow Latrodectus mactans mena vody and the brown widow Latrodectus geometricus. From March 1991 through July 1992, 10 cases of envenomation by these spiders were treated in the Intensive Care Unit of Antananarivo Hospital. Symptomatology was remarkable with regard to severity (one fatality due to cardiovascular failure, one gangrene of the foot) as well as clinical manifestations (immediate local pain, kidney dysfunction, arterial hypertension). In two cases, the spider was captured and identified. Both were female brown widows (Latrodectus geometricus), which might explain the differences observed in comparison with the classic features of latrodectism that have been established from American and European black widow bites. Since antivenom was unavailable, only symptomatic treatment was administered, including intravenous calcium that proved effective for pain relief.