Thirty patients with malignant melanoma and cerebral metastases confirmed by CT were studied. Metastases were classified according to their size: < or = 1 cm (group A), 1.1-4 cm (group B), and > 4 cm (group C), in order to assess the clinical course of the disease and predict the response to treatment with fotemustine. Group B lesions were the most common, independent of the site of the primary tumour, except for patients with rectal melanoma. Group C metastases were least common and were usually solitary. Asymptomatic patients usually had group A metastases, whereas those with non-specific complaints, hemisyndrome or neurobehavioural changes usually had group B metastases. The time from diagnosis of the primary tumour to discovery of disease in the CNS was significantly longer for those who had group A lesions, compared with those who had groups B or C lesions (P < 0.0001). Solitary lesions usually belonged to groups B or C, whereas multiple lesions belonged mainly to groups A or B. All the responders to fotemustine has mainly cortical, group A or group B lesions. Patients with group C lesions or leptomeningeal spread did not respond to fotemustine. Our findings suggest an association between the size of the cerebral metastatic lesion from malignant melanoma and clinical parameters characteristic of tumour behaviour.