Thoracic endometriosis is a rare condition and occurs in females of reproductive age due to the presence of active endometrial tissue in tracheobronchial tree, lung parenchyma and lung pleura. A typical history of haemoptysis during menstrual periods and strong suspicion of the disease entity is important for the diagnosis and management of the case. Diagnosis of the disease is usually delayed. Serial CT thorax during menstrual period and in non-menstrual period supports the diagnosis. We present here a case of catamenial haemoptysis. The diagnosis was missed initially but later a detailed clinical history revealed the same. Serial computed tomography of thorax taken during menstrual and after menstrual period supported the diagnosis. Though bronchoscopy was able to reveal hyperemic tissue in the tracheobronchial tree, bronchial washing was inconclusive. The patient was treated successfully with danazol.