The authors summarize contemporary knowledge on the incidence, genesis and therapy of colloid cysts of the third ventricle and present three of their own cases. Although a benign tumour is involved, its site close to important brain centres and its relation to pathways of cerebrospinal fluid explains its clinical importance. 20 % of these cysts are diagnosed late and the first symptom may be coma or sudden death. Recently new findings on its histogenesis were discovered, regarding surgical treatment (incl. stereotactic exhaustion of the contents of the cyst) and its occurrence in children as the cause of sudden death.

        Key words: colloid cyst, intraventricular tumours, transfrontal microsurgery, stereotactic aspiration