The reproductive cycle of the white eared opossum Didelphis albiventris Lund was studied in an area of temperate climate conditions in the region of Buenos Aires Province, Argentina. In 1987–1988 and 1988–1989 the reproductive season began in late August and continued until mid-March. Two distinct breeding periods per season were evident, the first in early September and a second in December. Litter size ranged from 4 to 9. The sex ratio in the pouch was 1:1. Only those females that gave birth early in the season could produce a second litter in December. Progressive pouch mortality was not found. Young opossums were weaned at 3.5 months of age and remained sexually inactive until the next reproductive season. Ages of captured opossums suggest that few animals survive for more than 20 months. Therefore, in the study area, most specimens breed only during one reproductive season. In South America, a latitudinal cline in the timing of the breeding season extends from tropical to temperate areas.