A 10-year-old boy with the history of headache, anorexia, and vomiting was referred to our department to undergo a brain CT scan. CT images demonstrated a well-defined, rounded, hyperdense lesion at the level of the foramen of Monro causing moderate dilatation of the lateral ventricles. An 11-year-old girl with a long history of a headache was also referred to undergoing a brain MRI. MR images demonstrated a well-defined round abnormal signal intensity lesion at the level of the foramen of Monro causing moderate dilatation of lateral ventricles. The findings from imaging perspective were consistent with the colloid cyst of the third ventricle. Therefore, the diagnosis of the colloid cyst was made.