BACKGROUND. Studies evaluating the efficacy of routine follow-up testing in detecting disease recurrence in treated lung carcinoma patients are lacking. METHODS. To investigate this subject, the authors studied 115 patients who had previously been entered on North Central Cancer Treatment Group (NCCTG) small cell lung carcinoma clinical trials, had achieved a complete response after chemotherapy/radiotherapy treatment, and subsequently developed disease progression. The authors included 58 patients with limited stage and 57 patients with extensive stage disease. Follow-up testing on these clinical trials was scheduled at 4-month intervals in the first year and every 6 months thereafter. At each visit, testing included a clinical history, physical examination, chest X-ray, chemistry group, and hematology group. Patients' records were evaluated to determine the first test(s) to identify disease recurrence, whether the recurrence was diagnosed at the time of routine follow-up or between scheduled follow-up evaluations, the sites of recurrence, and patient outcome. RESULTS. Recurrences occurred in 56 patients (49%) in the first follow-up year, 51 (44%) in the second year, and 8 (7%) after 2 years. Recurrences were signaled by clinical histories in 71% of patients, by physical examinations in 10%, chest X-rays in 12%, and abnormal chemistry testing in 6%. Although 41% of recurrences were detected at scheduled clinical visits, 59% of patients had disease recurrence signaled by symptoms that prompted interval visits between scheduled appointments. At last follow-up, all the patients in this study had died (median survival, 115 days [range, 1-793 days] after diagnosis of recurrence), supporting the lack of curative therapy for patients with recurrent small cell lung carcinoma. CONCLUSIONS. These data, demonstrating that clinical histories and physical examinations are the most fruitful means of detecting evidence of recurrent lung carcinoma, are consistent with data regarding the follow-up of other curatively treated cancers, such as breast carcinoma and melanoma. Chest X- rays in asymptomatic patients detect recurrences in a small proportion of patients, whereas routine blood tests appear to be of little value.