The planum temporale (PT) is a highly lateralized cortical region located within Wernickes area which is thought to be involved in auditory processing, phonological processing, and language. Research has linked abnormal morphology of the PT and its parietal extension, the planum parietale (PP), to developmental dyslexia, although results have varied in large part due to methodological inconsistencies in the literature. This study examined the asymmetry of the PT and PP in 29 children who met criteria for dyslexia and 26 children who did not. Leftward asymmetry of the PT was found in the total sample, and this leftward asymmetry was significantly reduced in children with dyslexia. This reduced leftward asymmetry in children with dyslexia was due to a PT that is larger in the right hemisphere. In this sample, leftward PT asymmetry was significantly correlated with right-handedness, but not with verbal intelligence or phonological processing. Furthermore, PT asymmetry did not predict reading achievement. Significant results were not found with regard to PP asymmetry. This study lends support to the idea that PT asymmetry is altered in children with developmental dyslexia.