A father and daughter with colloid cysts of the third ventricle are described. The nine previously reported examples of familial occurrence are reviewed, and the conclusion is reached that inheritance is likely autosomal dominant. The proportion of all cases which are genetic is not known. A plea is made for routine detailed and thorough family histories on all patients with such cysts and a high index of suspicion for non-specific symptoms in relatives such as headaches, migraine, depression, anxiety, nausea and vomiting.