Mycoplasma pneumoniae is an important etiologic agent of acute childhood encephalitis. We retrospectively reviewed 17 cases of M. pneumoniae encephalitis at the Pediatric Department of the National Taiwan University Hospital from April 1997 through March 2000. These cases were diagnosed as having positive immunoglobulin M antibodies (94%), a minimum 4-fold change of complement-fixation antibody titers (47%), or nested polymerase chain reaction. The ages of these patients ranged from 1.5 to 10.9 years (mean, 5.3 years) with a male-to-female ratio of 8:9. The clinical manifestations included fever (94%), altered consciousness (65%), seizure (41%), personality or behavior changes (29%), meningeal sign (24%), visual hallucination (24%), ataxia (12%), Guillain-Barré syndrome (6%), blurred vision (6%), and aphasia (6%). Respiratory symptoms and signs were found in 76% of the patients. Abnormal electroencephalogram and neuroimage were observed in all cases, while abnormal cerebrospinal fluid examination was noted in about one-third of the patients. Five (29%) patients required intensive care because of intractable seizure or respiratory failure. Fourteen (82%) patients recovered completely, but 3 (18%) had sequelae including epilepsy, hydrocephalus, and global neurologic deficits with brain stem dysfunction. In Taiwan, M. pneumoniae should be considered an etiologic pathogen of acute childhood encephalitis if fever and respiratory symptoms and signs are observed with or without abnormal cerebrospinal fluid findings. Supportive treatment is the basis of management.