Sitamaquine (WR6026) is an 8-aminoquinoline in development for the oral treatment of visceral leishmaniasis (VL). This was an open-label, dose-increasing study to determine the dose-response and safety profile for sitamaquine in Kenyan patients with VL caused by Leishmania donovani. Patients (mean age 15.9 [range = 5-47] years) received sitamaquine daily for 28 days at one of four doses: 1.75 (n = 12), 2.0 (n = 61), 2.5 (n = 12), or 3.0 (n = 12) mg/kg/day. The primary efficacy outcome was cure (absence of parasites on splenic aspirate) in the intent-to-treat population at day 180. Cure was achieved in 79 (83%) of 95 patients overall, and in 11 (92%) of 12, 49 (80%) of 61, 9 (82%) of 11, and 10 (91%) of 11 patients at sitamaquine doses of 1.75, 2.0, 2.5, or 3.0 mg/kg/day, respectively. The most frequent adverse events during active treatment were abdominal pain (12 [12%] of 97) and headache (11 [11%] of 97), and one patient in each of the 2.5 mg/kg/day and 3.0 mg/kg/day dose groups had a severe renal adverse event. The effects of sitamaquine on the kidney need further investigation. Sitamaquine was efficacious and generally well tolerated in Kenyan patients with VL.