Subacute sclerosing panencephalitis (SSPE) is diagnosed with clinical evaluation including history and physical evaluation along with electroencephalogram (EEG), magnetic resonance imaging of the brain and cerebrospinal fluid (CSF) analysis. A total of 3 patients with SSPE (mean age= 25.3 years) who were admitted to the Department of Neurology at Uludag University Faculty of Medicine, were evaluated retrospectively. Clinical staging was performed using Risk and Haddad's classification. Time to SSPE diagnosis from initial symptoms ranged from 10 days to 3 months; the patients presented to a physician two months after their symptoms were recognized; weakening of mental capacities attracted the attention of members of their families. EEG examinations revealed slow baseline activity and penetrating slow discharges with regular high amplitudes every 8-10 seconds. Although immunoglobulin (Ig) M for measles was negative, IgG was positive in the cerebrospinal fluid and serum samples of all patients. All patients received isoprinosine, and various doses of valproic acid and clonazepam during their treatment. One patient died 13 months after the diagnosis, the other two continue to be followed up. SSPE infection should be considered in central nervous system-involved rapidly-progressing late-onset adult diseases because there has recently been a rapid increase in the number of reported cases of SSPE.