A thirty four year old woman with recurrent catamenial pneumothorax is described. Pleural endometriosis was suspected and cytologic examination of fluid drained from the right pleural cavity showed glandular cell clusters of probable endometrial origin. The patient received a long-acting GnRH agonist (Triptorelin-Arvekap-Ipsen) 3.75 mg/month I.M. for nine months and remains asymptomatic with regular periods 12 months after discontinuing the treatment.