Forty-five children with acute lymphoblastic leukemia or non-Hodgkin's lymphoma had cranial nerve palsy (CNP) as a complication of their disease. Twenty-two of these children had CNP initially and 23, at relapse, with or without previous hematologic relapse. Only one of the 23 patients with CNP at relapse was a long-term survivor. In contrast, 11 of the 22 children who had CNP initially survived in remission for 3+ months to 13+ years. Two factors are associated with an improved outcome for patients with CNP at diagnosis: treatment after 1979 (P less than 0.004) and male gender (P less than 0.01). Patients who received radiation therapy fared better than those for whom radiation was not given (disease-free survival at 2 years 53% versus 29%). The authors conclude that CNP signifies an aggressive or advanced disease requiring intensive systemic chemotherapy and that the role of irradiation should be examined for this group of patients.