We assessed the efficacy and safety of a seven-day course of artesunate for the treatment of uncomplicated Plasmodium falciparum malaria in 55 non-immune patients living in Bangui, Central African Republic. The parasitologic cure rates were 100%, 95%, and 85% on days 14, 28, and 42, respectively. There were no significant differences in parasitemia density, 50% inhibitory concentration of dihydroartemisinin, and frequency of mutant P. falciparum multidrug resistance 1 codon 86 between patients who were cured and those who displayed recrudescence. However, the 90% inhibitory concentration for dihydroartemisinin and the number of genotypes isolated were both higher in the recrudescent patients (five- and two-fold, respectively). We found an association between recrudescence and decreased sensitivity. This suggests that the use of artemisinin compounds alone will select resistant strains. We conclude that artesunate should not be used in monotherapy even in seven-day courses, but only in combination with other anti-malarials to prevent the emergence of resistant P. falciparum.