One-hundred forty-six SCLC patients were classified as localised (56) or extensive (90) using chest X-ray, bronchoscopy, brain CT, bone scintigraphy, ultrasonography of the abdomen and bilateral bone marrow trephine biopsy. Bone marrow metastases were found in 28 cases. Patients with bone marrow metastases had significantly shorter time to progression (median 20 weeks) and significantly shorter survival time (median 31 weeks) than other patients with extensive disease (medians 30 and 46 weeks). Patients with bone marrow involvement had significantly more often metastases in three or more organs than others with extensive disease. The negative prognostic significance of bone marrow involvement was however independent of the negative prognostic significance of the number of organs with metastases.