A new method of assessment based on mid-upper arm circumference (MUAC) is described for dosage adjustment for community-based ivermectin distribution. We studied 878 subjects eligible for ivermectin dosing in Awhum, Nigeria. In a previous preliminary study of 40 persons, MUAC (in cm) correlated with weight (kg) in the first 20 male (r = 0.97, r2 = 0.95, P < 0.0001) and the first 20 female subjects (r = 0.94, r2 = 0.88, P < 0.0001). We therefore studied the use of height, physical appearance, and MUAC for calculating the dose of ivermectin. The MUAC-based schedule underdosed only 4.1% of the population. The methods based on height underdosed 3.3% and 21.1%, and assignment based on physical appearance underdosed 10.2% of the population studied. This MUAC-based method (13-15 cm, 0.5 tablet; 16-20 cm, 1.0 tablet; 21-27 cm, 1.5 tablets; > or = 28 cm, 2.0 tablets) is more convenient and corresponds closely to dosing by weight. An adaptation of this method with reference to other prevalent tropical diseases and their respective drugs is therefore advocated.