Ethanol exposure during development has been shown to alter social behaviors in people, but the range of deficits is not clear. Using an animal model of Fetal Alcohol Spectrum Disorders, inter-male aggression and testosterone levels were examined in adult rats. Rats were exposed to ethanol during the entire prenatal period and from postnatal day 2 through 10. Ethanol was administered via intragastric intubation. Two other groups consisted of a nontreated control and an intubated control group that was exposed to the administration procedures but not ethanol. Both offensive and defensive aggression were examined in experimental residents and intruders under three different housing conditions for the resident males: (1) with another male, (2) with a pregnant female, and (3) with a female and litter fathered by the experimental animal. When housed with a female and litter, ethanol-exposed rats displayed reduced offensive aggression compared to control groups under the same condition. Defensive aggression in the non-experimental intruders was reduced in this same condition. There were no differences in duration of non-aggressive social behaviors among the groups in any of the housing conditions. Testosterone levels were reduced in ethanol-exposed rats compared to controls. In summary, ethanol exposure over the combined prenatal and postnatal periods reduces aggressive behavior in a condition where aggressive behavior is normally seen. This reduction may be related to lower testosterone levels.