We report the case of a man of aged 27 years who presented with obstructive hydrocephalus caused by a colloid cyst of the third ventricle. He was found to have an additional and larger colloid cyst lying adjacent to it, but within the lateral ventricle. The contents of the two cysts were of different consistency. We have been able to find only one previous report of more than one colloid cyst occurring in the same patient and none where one of the cysts lay within the lateral ventricle.