In 1983, the first African cases of malaria due to Plasmodium falciparum resistant to sulfadoxine/pyrimethamine, were described. Currently, this resistance is frequently found in Kenya and Tanzania. It has also been described in other African countries. A young Spanish woman contracted Plasmodium falciparum malaria in Senegal and was treated in our hospital with sulfadoxine/pyrimethamine. Fever and symptoms disappear within two days. The thick smears taken on the eighth and thirteenth days of treatment contained an abundance of gametocytes, but neither trophozoites nor schizonts. As the risk of transmission of malaria to the rest of the community was considered practically nil, no other treatment was administered. A month late, she was admitted to the hospital due to fever, shivering, fatigue, loss of appetite and hemolytic anaemia. The thick smear test again showed trophozoites of P. Falciparum. Thus, it proved to be a delayed grade I resistance to sulfadoxine/pyrimethamine, detected in far west Africa. An oral dose of mefloquine was administered as well as a red cell transfusion. Both fever and symptoms finally disappeared.