The Patterns of Care Study (PCS) conducted a nationwide audit survey in order to establish the national practice process of radiation therapy for small-cell lung cancer (SCLC) and examined the influence of institutional stratification on the process of care in Japan. The PCS randomly sampled institutions and patients using a two-stage cluster method and surveyed the process of radiation therapy for 174 stage I-III SCLC patients according to the category of institution, stratified as follows: A1, academic institutions treating > or = 300 patients a year; A2, <300 patients; B1, non-academic institutions treating > or = 120 patients a year; and B2, <120 patients. Karnofsky performance status distributions showed significant variance by stratification of institutions (P=0.013). Patients treated on an outpatient basis accounted for 32% in A1, 23% in A2, 8% in B1, but only 5% in B2 (P=0.007). A photon energy > or = 10 MV was used for 87% of patients in A1, 69% in A2, 54% in B1 and 23% in B2 (P=0.001). Contralateral hilus was irradiated for 11% of patients in A1, 17% in A2, 29% in B1 and 3% in B2 (P=0.001). Field size reduction during the treatment course was done for 77% of patients in A1, 54% in A2, 60% in B1 and 42% in B2 (P=0.007). Ninety-two percent of patients received combined chemotherapy and radiation therapy, and the most frequently used drugs were etoposide (91%) and cisplatin (69%). The results of clinical studies on SCLC had favorably penetrated into the clinical practice. However, the stratification of institutions significantly affected the process of radiation therapy in Japan.