The present study examined the systematic effects of gender and situation on two personality characteristics: dominance and friendliness. Individuals were observed twice in each of three situations: with a familiar person of the same sex, with an unfamiliar person of the same sex, and with an unfamiliar person of the opposite sex. Observations by independent observers were collected using behavior counts and ratings. In addition, selfreports about dominance and friendliness in different situations were collected. Results based on the independent observers generally indicated that sex differences are reduced in mixed-sex groups and accentuated in same-sex groups. There was also evidence of systematic errors in the self-reports suggesting that men may overestimate their degree of friendliness and that women may overestimate their level of dominance.