Colloid cysts of the third ventricle are benign lesions that occur in 0.5 -2% of cases, and are usually identified in adolescence or early adulthood, due to the symptoms they produce (headache, nausea or symptoms of intracranial hypertension caused by the accumulation of cerebrospinal fluid). Diagnosis is made by brain magnetic resonance imaging. In a 30-year-old primigest, a partial absence of the cavum of the septum pellucidum (ASP) was observed in the axial planes at 22 weeks. Fetal DNA was negative for Trisomies 21, 18 and 13. STORCH group infections were ruled out. Advanced neurosonography at 26 weeks: chiasm and optic tracts; thalami, ventricles, cerebellum and sulcular patterns were interpreted as appropriate-for-gestational age. Brain MRI at 28 weeks confirmed ASP with no other associated abnormalities. She delivered a boy at 38 weeks of gestational age with spontaneous adaptation and a weight of 3035 grams. Postnatally, brain MRI findings with emphasis on the sella turcica showed persistence of the septum pellucidum cavity and an image indicative of a colloid cyst of the roof of the third ventricle. Endocrine and visual studies were performed and were normal. A septal septo-optic septal dysplasia DSO was ruled out. The four-month-old boy is currently under multidisciplinary neurodevelopmental follow-up by a team consisting of neurology, endocrinology, ophthalmology and genetics. Serum testing of the hypothalamic-pituitary axis was performed. Colloid cysts are benign congenital intracranial lesions of the anterosuperior portion of the third ventricle that interrupt the free flow of cerebrospinal fluid (CSF), by intermittent or prolonged obstruction of the foramen of Monro and accumulation of CSF and may cause hydrocephalus. The growth rate of the colloid cyst is uncertain, it is not possible to predict which colloid cysts will become symptomatic. They should have multidisciplinary follow-up and management according to symptomatology with neurosurgery.