Signet ring cell carcinoma has been previously described in many organs, most frequently in the stomach, and rarely in the colon, rectum, gallbladder, pancreas, breast, nadsal cavity, prostate, urinary bladder and ureter. Signet ring cell carcinomas in the lung, especially, when examined by small biopsies, are generally believed to be metastatic. This case was diagnosed by bronchoscopic biopsy. We also examined various organs by noninvasive method, including UGI series, barium enema and abdomen CT scarf, but all studies were nomal. Patient received cisplatin and etoposide combination chemotherapy followed by local radiotherapy ai a primary non-small cell lung cancer. Patient died of his disease 6 months after diagnosis. Now we report a case of primary signet ring cell carcinoma of the lung.