Forty-one patients with two subtypes of stage IIIM0 non-small-cell lung cancer treated over a 7-year period were evaluated. The first group of 20 patients had ipsilateral parietal pleural involvement not contiguous with the primary tumor but no distant metastases. Fifteen had positive pleural fluid cytology, seven with positive pleural biopsy in addition; four had extensive pleural studding or a positive biopsy but no effusion; and one had negative pleural fluid cytology. Treatment consisted of radiation therapy followed by combination chemotherapy in all. Due to symptoms, eight patients first had fluid drainage with or without sclerosis and two patients had a pleurectomy. Nine had progressive pleural disease despite the local treatment. To all modalities of therapy, only two patients had a partial response. One patient who had a pleurectomy lived 25 months. Median survival was 6.9 months. Cause of failure involved local progression in 17 patients. There was no difference in median survival by age, sex, histology, side of effusion, location of nodal disease, or use of local therapy. The second group of 21 patients had localized involvement of the parietal pleura by the primary tumor. There was deeper chest wall invasion in nine. All patients were rendered free of known disease by surgical resection, were stage T3N0-2M0, and received radiation and chemotherapy in addition to resection. The median survival was 13.5 months. There was local recurrence in nine patients but only one developed an effusion. Five patients were alive at 29-82 months. No variable unfavorably influenced survival except a central versus peripheral primary. Thus, the median survival of the patients in the first group with multiple sites of pleural involvement was similar to that of patients with distant metastases but with the cause of failure primarily local progression. In the majority of patients in the second group, parietal pleural and chest wall involvement, even with nodal metastases, did not translate into local failure, and long-term survival was possible.