Endometriosis in less common locations can become a diagnostic pitfall both from the clinical and morphological point of view, as this diagnosis is only seldom considered in the first series of differential diagnoses. This was true also for our patient reported. 48-year-old woman underwent left superior lobectomy for the clinical diagnosis of pulmonary neoplasm. Slightly prominent subpleural whitish nodular partly cystic tissue was histologically identified as pulmonary endometriosis. It consisted of proliferative to hyperproliferative endometrial glands surrounded by proliferation type stroma. Focally slight cytological glandular atypias and immature squamous metaplasia were present. Later another focus was located by x-ray examination. Without any surgery, it responded to six month treatment with competitive gonadoliberin agonist (GnRH analogue) Zoladex. Three years after the treatment no signs of the disease have been present. The correct clinical diagnosis accompanied with cautious morphological verification may prevent unnecessary extensive surgery. However, even some correctly diagnosed and morphologically verified cases may require radical operative removal. Either approach (conservative therapy and surgery) completed with subsequent dispensarisation may prevent both the common (cycle related progressive tissue damage) and rare (tissue destruction, malignant transformation) complications.

        Key words: pulmonary endometriosis, lung pseudotumours, long neoplasm, catamenial haemothorax, catamenial haemoptysis.