From 1979 to 1992, of 1,294 patients with esophageal squamous cell carcinoma, 39 patients (3.2%) (38 male patients, 1 female patient; mean age, 58 years) had associated primary lung carcinoma. Criteria for the diagnosis of primary lung carcinoma were: (1) non-squamous cell carcinoma tumors, (2) tumors existing before the esophageal squamous cell carcinoma, and (3) solitary squamous cell carcinoma presenting with endobronchial involvement. The two tumors were observed synchronously in 22 patients (56%) and metachronously in 17, with a mean tumor-free interval of 46 months (range, 18 to 77 months). In patients with synchronous disease, 10 underwent nonoperative treatment or a palliative surgical procedure, and 12 (55%) underwent a curative operation. In patients with metachronous disease, a curative operation was performed in all for the first tumor and in 9 (53%) for the second tumor. The overall postoperative mortality rate was 15%. Two patients (10%) died after the curative operation. None of the patients died who underwent curative esophagectomy combined with lobectomy. For the patients with synchronous disease, the 5-year survival rate was 11% in those who underwent a curative operation, and the longest survival in those who received palliative treatment was 18 months. For the patients with metachronous disease, the 5-year survival rates from the date of the diagnosis of the second tumor were 17% for those who had a curative operation and 11% for those who received palliative treatment.(ABSTRACT TRUNCATED AT 250 WORDS)