It has been hypothesized that cerebral lateralization can significantly enhance cognition and that this was one of the primary selective forces shaping its wide-spread evolution amongst vertebrate taxa. Here we tested this hypothesis to examine the link between cerebral lateralization and numerical discrimination. Guppies, Poecilia reticulata, were sorted into left, right and non-lateralized groups using a standard mirror test and their numerical decimation abilities tested in both a natural shoal choice and abstract contexts. Our results show that strongly lateralized guppies have enhanced numerical abilities compared to non-lateralized guppies irrespective of context. These data provide further credence to the notion that cerebral lateralization can enhance cognitive efficiency