Thirty-one (23%) of 137 patients treated for leptomeningeal metastases (LM) achieved a sustained off-therapy response of at least 6 months' duration following treatment by a standard protocol. Of the 31 patients, equal distribution was found among various tumors: lymphoma, 13/44 (29%); breast carcinoma, 10/51 (20%); and other tumors, 8/42 (19%). Neuroimaging of the neuraxis disclosed subarachnoid deposits in 70%, with unexpected findings in 55%. At withdrawal of therapy, all 13 patients with lymphomas had achieved a complete response, and for those with the other tumors, 61% had a partial response. Off-therapy relapse was unrelated to the type of attained response and occurred in nine patients (29%) after a median time of 12 months. Five patients obtained a second prolonged response, mainly by systemic therapy. All eight patients who received only systemic therapy for their LM responded to treatment, four with a complete response. All others received both systemic and intra-CSF treatment and maintained a systemic response. Delayed complications occurred in 58%, with leukoencephalopathy equally affecting patients exposed and patients not exposed to cranial irradiation. The median survival of the whole group was 23 months. We conclude that in LM (lymphomas excluded), a partial response is compatible with a prolonged off-therapy response. Since LM may respond to systemic treatment, the role of intra-CSF therapy, with its associated complications, deserves a prospective reevaluation.