Incomplete hippocampal inversion (IHI) is an atypical anatomical pattern of the hippocampus. It has been mostly described in patients with epilepsy, in particular with malformations of cortical development but also in temporal lobe epilepsy (Baulac et al. 1998; Bernasconi et al. 2005; Bajic et al. 2009), with a prevalence of 30%-50%. However, IHI are also found in healthy subjects, although with an apparently lower frequency (Bajic et al. 2008). A few studies have investigated the prevalence of IHI in subjects without seizures (Gamss et al. 2009; D. Bajic et al. 2008). However, these studies include a small number of subjects leading to an imprecise estimation of the prevalence of IHI, or included patients without epileptic seizures but referred for other neurological conditions. Therefore, the frequency of IHI in healthy subjects remains unclear.The purpose of our study was to investigate the prevalence of IHI in a large population of healthy subjects.