We have compared the performance of male and female Wistar rats at different ages (45, 60, 90, 120 and 150 days) in the elevated plus-maze test, a reliable animal model of anxiety. Up to 60 days of age, rats of both sexes exhibited a high number of entries and of time spent on open arms (50% or above). At 120 days of age or more, rats of both sexes characteristically exhibited a reduction in the number of entries and of the time spent on open arms (below 50%). Within the range of 60 and 120 days there are statistically significant sex differences. At 90 days of age male rats showed a marked switch in their performance in the apparatus, reaching levels of the latter stage, whereas in females it happened around 120 days. These results suggest an ontogenetic difference in rats that accounts for at least two distinct performances for rats placed in an elevated plus-maze. Gender effects were found in a certain range, suggesting caution on interpreting data obtained in rats within 60 and 120 days old. Also, the results obtained highlight the importance of carefully controlling animal age in studies using the elevated plus-maze.