The efficacy of artemisinin monotherapy was studied in 227 patients with uncomplicated falciparum malaria. They all received artemisinin at t = 0 hr, t = 8 hr, and thereafter once daily; treatment was extended at random until they had taken either 5 days of artemisinin followed by 2 days of placebo (A5), or 7 days (A7) of artemisinin. The adult artemisinin dose was 500 mg; children aged < 15 years received 10 mg/kg per dose. The median (range) parasite clearance time was 39 (8-112) hr for A5 and 43 (38-104) hr for A7 (P = 0.085). The recrudescence rates were similar between the groups. The lowest parasite count achieved during treatment (Pterm) was associated with the occurrence of recrudescence (P = 0.046, Cox regression model); it was lower for patients with a radical cure or late recrudescence than for early recrudescence (P = 0.034, t-test). Artemisinin monotherapy may offer rapid recovery and fast parasite clearance, but recrudescence is frequent. Extending the duration of monotherapy from 5 days to 7 days does not reduce recrudescence.