Acute cerebellar encephalopathy (ACE)--ataxia often associated with opsoclonus, polymyoclonus, and irritability--may be associated with neuroblastoma and should be suspected in a child who presents with ACE. The survival in ten children with ACE associated with neuroblastoma was 100%. Most of the tumors were ganglioneuroblastomas. The abdomen was the most common location for the tumor in this study although it also can be found in the mediastinum. All patients with this syndrome had a localized tumor. With ACTH therapy, ACE may resolve early postoperatively, but it tends to recur in most patients, continuing for as long as 3 years after the initial operation. Treatment with ACTH or prednisone modifies and rapidly clears the symptoms during the acute episode of recurrent ACE as well as helps to resolve subsequent neurologic sequelae. Significant neurologic sequelae persisted in seven of ten patients and included deficits in cognition or intellect, hyperactivity, impulsivity, emotional lability, and mild motor deficits. Seizures were seen in one patient.