Subacute sclerosing panencephalitis (SSPE) is rare in Taiwan. On admission to hospital, a 15-year-old boy was diagnosed with SSPE based on the clinical picture, electroencephalogram, cerebrospinal fluid studies, and brain biopsy. The initial clinical picture was a decline in school performance and a change in personality, followed by progressive tic-like involuntary movements and mental impairment for 8 months, then a rapidly progressive course. After the patient was treated with oral inosiplex and intraventricular interferon-alpha (IFN-alpha), his condition stabilized and the neurologic disability index score improved slightly. There were no major side effects during treatment except for a transient initial elevation of body temperature that lasted for several days. Oral inosiplex and intraventricular IFN-alpha appear to be safe and effective. Early identification and aggressive treatment of SSPE is important.