Brain MRI scans revealed various occipital horn variants in a pedigreed baboon colony consisting of Papio hamadryas anubis and its hybrids. We retrospectively characterized these variants and evaluated their relationships to epilepsy phenotypes and scalp EEG findings. MRI scans (3D, T1-weighted) from 208 baboons (female, 134 female; male, 74; age [mean ± 1 SD], 16 ± 5 y) were reviewed; 139 (67%) of these animals also underwent scalp EEG previously. Occipital horn variants included elongation (extension of the occipital ventricle behind the mediobasal origin of the calcarine fissure), which affected 23 baboons (11%; 7 bilateral, 9 left, 7 right), and elongation with enlargement (colpocephaly), which occurred in 30 baboons (14%; 7 bilateral, 11 left, 12 right). The incidence of the occipital horn variants did not differ according to age or prenatal or perinatal history. Colpocephaly was associated with craniofacial trauma but not with witnessed seizures. Abnormal scalp EEG findings, including interictal epileptic discharges, did not differ significantly among the occipital horn morphologies. This study is the first radiologic description of occipital horn variants, particularly colpocephaly, in baboons. Whereas colpocephaly is frequently associated with other radiologic and neurologic abnormalities in humans, it is mostly an isolated finding in baboons. Because craniofacial trauma can occur in the setting of seizure-related falls, its increased association with colpocephaly may reflect an increased risk of seizures or of traumatic brain injuries due to seizures. Colpocephaly in baboons needs to be characterized prospectively radiologically, neurologically, histopathologically, and genetically to better understand its etiology and clinical significance.