The present study was designed to investigate self-posed smiling behavior in photographs as a function of both sex and age. The photographs of 1,171 Brazilian middle-class people, taken in a wide variety of informal social settings were examined. Only 25.7% of the girls and 25.0% of the boys of 2- to 5-yrs-age group were seen smiling in the photographs. Older children, adolescents, and adults were much more expressive than young children. Furthermore, significantly more females were seen smiling than males. Females also smiled more expansively than males. Finally, smiling was less frequent among middle-aged and older groups, especially among males. The present study replicated the sex difference in self-posed smiling behavior consistently reported by American researchers examining college yearbook photographs. Further, the results are consistent with the hypothesis that, besides being associated with emotional experience, smiling has a strong social motivation.