We studied the effects of male Aedes aegypti age, body size, and density on mating success under laboratory and field conditions. Older males under field conditions transferred the greatest number of sperm to females (1,152 by 1-day-old males to 1,892 sperm by 10-day-old males). Larger males inseminated females with more sperm than smaller ones. Male age, female body size, and density also influenced male mating success. Larger females successfully mated with males more often than smaller females, especially with older males (> 25 days old). Female insemination rates in small high-density laboratory cages (0.009 m(3)) were artificially high (81.6-98.7%) compared with rates (65.4-84.6%) in large low-density field cages (9 m(3)). This is the first study to systematically evaluate the effect of Ae. aegypti male body size and age on sperm transfer to females and the first one to evaluate the mating performance of males in a field setting.