The analysis of clinical determinants of long-term survival in small cell lung cancer was investigated in consecutive series of 469 patients included in prospective multicenter clinical trials from 1981 to 1985. Forty eight patients (19.2%) were alive after 2 years from initiation of therapy and among them 27 (5.8%) were disease free. The most important clinical determinants of long-term survival were: extent of disease, performance status and sex. 38 out of 243 patients with limited disease (15.6%) survived for 2 years or more as well as 10 out of 226 patients with extensive disease (4.4%, p less than 0.001), 33 out of 237 patients with WHO performance status 0 and 1 (13.9%), and 15 out of 232 patients with performance status from 2 to 4 (6.4%, p less than 0.01), 29 out of 229 (12.2%) with absence of weight loss before therapy and 19 out of 240 (7.9%) with weight loss (N.S.), 32 out of 392 males (8.2%) and 16 out of 77 females (20.7%, p less than 0.01). Out of 27 disease-free survivors 21 are alive with no sign of malignancy after 3.5 to 7 years from initiation of therapy. Ten patients out of 229 followed up for a minimum 5 years after inclusion to the studies survived this period with no signs of disease. This study confirms the possible curability of small cell lung cancer, especially in patients with favorable prognostic characteristic.