Williams Syndrome (WS) is described as displaying a dissociation within memory systems. As the integrity of hippocampal formation (HF) is determinant for memory performance, we examined HF volumes and its association with memory measures in a group of WS and in a typically development group. A significantly reduced intracranial content was found in WS, despite no differences were observed for HF absolute volumes between groups. When volumes were normalized, left HF was increased in WS. Moreover, a lack of the normal right greater than left HF asymmetry was observed in WS. No positive correlations were found between volumetric and neurocognitive data in WS. In sum, a relative enlargement of HF and atypical patterns of asymmetry suggest abnormal brain development in WS.