Epidermoid cysts may occur simultaneously above and below the tentorium. Eleven patients with involvement of both infra- and supra-tentorial cisterns are presented. In two cases the epidermoid, located mainly in the cerebello-pontine angle, spread into the middle cranial fossa; in three the epidermoid extended from the parasellar cisterns to the posterior cranial fossa; in six patients the epidermoid, enlarging the tentorial notch, occupied extensively both cranial fossae. The surgical approach was influenced both by the experience of the surgeon and by the main extension of the epidermoid. Total removal was feasible in two patients only but only one of the eleven patients had a recurrence of the epidermoid. The long term results appear to be unrelated to the size of the epidermoid and to the choice of approach.