Two hundred-twelve consecutive patients with small cell carcinoma of the lung were studied in order to correlate the risk of developing intracranial metastases to the initial stage of the disease (locoregional versus extensive) and to evaluate the prognostic significance of developing intracranial dissemination of the disease. Clinically detected intracranial metastases were observed in four percent at the time of primary diagnosis, and an additional 18 percent developed metastases during treatment. As regards clinically observed metastases during treatment, no difference was found between the two initial staging groups. Intracranial metastases without clinical evidence of progressive disease elsewhere were demonstrated in 10 out of 205 patients (5%). The median survival time after clinical presentation of intracranial metastases was 85 days for patients with locoregional disease versus 60 days for patients with extensive disease. A significantly shorter survival time was observed for patients with intracranial metastases at 0, 100, 200 and 300 days after start of treatment compared to patients still alive without metastases at those times. Brain autopsy was performed in 82 patients and was positive in 42 (51%). No statistical difference in the frequency of brain metastases was demonstrated when compared to the initial stage of the disease. No difference was observed between the two initial staging groups of patients with regard to risk of developing brain metastases. Autopsy substantiated that there was no difference between patients with and without brain metastases as regards survival. However, clinical intracranial metastases were followed by a short survival time, and only a small fraction of the patients developed clinically isolated intracranial relapse.