The efficacy of oral chloroquine was assessed in 268 children aged from 6 to 59 months attending pediatric services in regional hospitals between September 1997 and December 1998, located in the five county towns of the sanitary regions of the Central African Republic. Chloroquine was prescribed at 25 mg per kg body weight, and administered over 3 days to patients suffering from uncomplicated malaria. Body temperature and blood smears including parasitaemia were recorded on days 0, 3, 7 and 14. The main objective of the present study was to evaluate the therapeutic efficacy of chloroquine in the treatment of uncomplicated malaria using in vivo tests according to the WHO protocol (1996). The secondary objective was to identify the predictive factors of chloroquine relapses. Early relapses rates were under 15% except in Bangui (40%). A recurrence of parasitaemia with fever, sign of late relapse, was noted in 9% of children in Bambari, 9% in Bangassou, 8% in Bangui, 5% in Bossangoa and 4% in Berberati. The rate of successfully treated patients was between 66% and 75% except in Bangui (36%). Only the places of study and anaemia in days 0 were significant predictive factors of therapeutic relapses. Since the emergence of chloroquine resistance cases to P. falciparum in 1983 in Central African Republic, the phenomenon has increased. According to our results, a strong chloroquine resistance appears in the capital Bangui. Therefore, chloroquine should be replaced there for the first line treatment of uncomplicated P. falciparum malaria. In the provinces, it doesn't seem necessary to change the current chloroquine-based first line treatment.