Past studies suggest that males tend to be more dominant than females in task-oriented, mixed-sex groups. It was hypothesized that one factor accounting for this sex difference is performance-self-esteem. Subjects were 44 male-female pairs (college undergraduates) who participated in a decision-making task. As predicted, female performance-self-esteem level was related to the dominance cluster of opinions, disagreements, and decision outcome scores (p < .035). Females were more dominant and males less dominant in dyads containing high performance-self-esteem females; the reverse was true in dyads containing low performance-self-esteem females. No relationship was found between male performance-self-esteem level and dominance. Also, with performance-self-esteem level controlled, no overall sex difference in dominance occurred. However, some sex differences were found in the relationships between outcome satisfaction and dominance for high and low performance-self-esteem subjects.