Hamartia are small collections of rounded glioneuronal cells that are thought to be due to aberrant cell migration. Their presence has been recognized in association with mesial temporal lobe epilepsy; their prevalence among cases of hippocampal sclerosis (HS) and any potential association with patient demographics and outcomes is unknown. This study examines hamartia in a series of 292 patients with pathologically confirmed HS. Medical records were reviewed for pertinent patient clinical information (follow-up mean 5years). Hamartia were identified in 96 cases (33%) and were seen primarily in the amygdala (n=88) and less commonly in the hippocampus (n=10) and temporal lobe (n=4). A statistically significant relationship was found between the presence of hamartia and male gender, younger age of seizure onset, and history of childhood febrile seizures and developmental delay. It is unclear if these associations represent a real association or are a result of the underlying pathologies related to chronic epilepsy. At follow-up, there were no significant differences between patients who had hamartia and those who lacked this finding. Hamartia were observed in all subtypes of HS and there was a significant difference found in subtype distribution as well as proportion of cases between subtypes, but no association with any specific subtype overall. The presence of hamartia was not associated with the coexistence of focal cortical dysplasia or any specific histologic pattern of dysplasia. Hamartia are a common concomitant finding in HS and indicates evidence of aberrant cell migration in the hippocampal and parahippocampal regions in these patients.