When males and females differ in their spatial ecology, selection is expected to promote sex differences in spatial abilities. Although this prediction applies to many species, few studies have looked at sex differences in spatial abilities outside mammals. Here, we addressed this hypothesis in the guppy, Poecilia reticulata, a polygynous fish in which males disperse more than females and inhabit more spatially complex environments. We compared the performance of male and female guppies in two spatial tasks to test whether males have been selected for enhanced spatial abilities. In a detour task (experiment 1), the two sexes showed similar ability to navigate around an obstacle to reach a target. However, males were more persistent in trying to pass through the transparent obstacle, an effect that is likely to be related to sex differences in cognitive flexibility rather than to spatial abilities. In the second experiment, with a more complex maze in which guppies had to choose between alternative routes to reach the target, males learned the task after only one presentation, whereas females did not show any evidence of learning after five trials. The direction of these differences is the same as that observed in most polygynous species investigated, suggesting a common pattern of cognitive sex differences across vertebrates.