BACKGROUND: Myelomeningocele is the most common type of spina bifida and it is associated with hydrocephalus in 35% to 90% of cases. Hydrocephalus may be present at birth or develop following repair of myelomeningocele (latent). The risk of developing hydrocephalus post myelomeningocele repair could be determined by the use of preoperative clinical and trans-cranial ultrasound parameters. OBJECTIVE: To determine the risk of developing hydrocephalus after repair of myelomeningocele using preoperative clinical and trans-cranial sonographic parameters. METHODOLOGY: This prospective study was carried out from November 2016 to July 2018. Twenty-eight patients with myelomeningocele presenting to Lagos University Teaching Hospital (LUTH) were recruited. The patients had trans-cranial ultrasound at presentation and subsequently had repair of myelomeningocele. They were then followed up monthly for six months after repair for the development of hydrocephalus. Analysis of the state of the anterior fontanelle at presentation, the occipitofrontal circumference and pre-operative ventricular index, lateral ventricular ratio, bicaudate diameter, thalamo-occipital distance and maximum lateral ventricular diameter was done to determine their predictive values in the development of hydrocephalus after myelomeningocele repair before surgery for hydrocephalus. RESULTS: The age of the study population ranged from 1 -120 days with a mean of 20 days and the average age at the time of myelomeningocele repair was 23 days. There were 16(57.1%) females and 12(42.9%) males in the study. More males (7) 58.3% compared to females (2) 25.0% developed hydrocephalus after repair of myelomeningocele, however, this was not statistically significant (p=0.07). The OFC range at presentation was 31-42cm with a mean of 34.7cm ±2.6 SD. The probability that a patient will develop hydrocephalus after myelomeningocele repair increases by 1.74 times for 1cm increase in the occipito-frontal circumference (OFC) above 34.5cm before myelomeningocele repair, with the odds being 17.4%. This was found to be statistically significant (p=0.03). However, the state of the anterior fontanelle as well as the bicaudate diameter, ventricular index, thalamo-occipital distance, lateral ventricular ratio and lateral ventricular diameter were not found to be predictors of hydrocephalus post myelomeningocele repair, p value ≥0.05. CONCLUSION: The study revealed that the occipito-frontal circumference of the patients before myelomeningocele repair was predictive of development of hydrocephalus post repair while the state of the anterior fontanelle was not. Furthermore, pre-operative transfontanelle ultrasound parameters such as ventricular index, lateral ventricular ratio, bicaudate diameter, thalamo-occipital distance and lateral ventricular diameter were not predictors of hydrocephalus post myelomeningocele repair.