A circular focus of 1 cm diameter was discovered by chance on a thoracic x-ray of a female patient of 66 years of age suffering from chronic interstitial nephritis due to analgesics. Bronchoscopic suction revealed histologically a small-cell carcinoma of the lung but there was no indication of formation of metastases. The patient refused any tumor-specific treatment. In the further course of the disease the focus showed up radiologically for seven months and was then no longer visible throughout the following 14 months. The patient finally died subsequent to an extensive posterior myocardial infarction. Postmortem examination excluded the presence of a primary tumor of the lung or metastases. Our case suggests the rare occurrence of a spontaneous regression of a small-cell bronchial carcinoma. Although spontaneous regression of malignant diseases is ascribed to immunological factors, such regression can also occur if the immunological system is impaired, as had been the case in this particular patient with chronic renal insufficiency.