Subacute sclerosing panencephalitis (SSPE) caused by persistent defective measles virus strains, is a progressive neurological disorder of children and adolescents. The aim of this letter was to share the data from SSPE-suspected cases who were definitely diagnosed by the detection of increased antibody index in serum and cerebrospinal fluid (CSF) samples. A total of 11 patients (mean age: 14.3 years) with suspected SSPE between February 2006 to August 2008, were included in the study. Simultaneously obtained serum and CSF samples from patients were analyzed in terms of albumin, total IgG and measles-specific IgG levels (Measles Virus IgG ELISA for CSF Diagnostics, Euroimmun, Germany). The value of CSQ(rel) (relative CSF/serum quotient) >= 1.5 was accepted indicative for intrathecal measles antibody synthesis. Seven (63.6%) of the 11 patients' diagnosis were confirmed with the demonstration of elevated CSF/serum indices (CSQ(rel), range: 2.3-36.9; mean: 12.9). Mean age of those seven cases was 12.3 years (age range: 7-21) and four of them were male. The history of patients with high antibody indices indicated that three of four patients who had measles infection had not been vaccinated against measles. These three unvaccinated patients had measles infection at 3rd, 8th and 30th months of age, respectively, and the period of SSPE development were 15, 6 and 4.5 years, respectively. With this letter we would like to emphasize once more that effective measles vaccination is the only way for the prevention of measles and SSPE and the demonstration of increased measles antibody index in simultaneously obtained serum and CSF samples is crucial for the diagnosis of SSPE.