The number of cases of malaria imported to western Europe from tropical areas is steadily growing, due to the increased number of people traveling to endemic regions and to the spread of Plasmodium strains resistant to chemoprophylaxis. This has prompted the WHO to frequently update its guidelines concerning preventive therapy. We report on 143 consecutive cases of benign attacks of malaria in patients returning primarily from western and central Africa. Plasmodium falciparum was responsible for 80% of the cases. Forty-one percent of the patients had followed their preventive regimen correctly; mefloquine failed in 3 of them. Three early relapses were observed after curative treatment, including 2 patients who had received intravenous quinine for more than 5 days. Because P. falciparum infection is potentially lethal, we suggest that the treatment of malaria attacks be optimized, by systematically dosing serum quinine levels, in order to adjust the administered doses, and, as a first-line therapy, by prescribing a combination of drugs to patients at high risk of resistance.