The aim of the present study was to confirm the frequency of microsatellite instability in thyroid cancers. We investigated 26 patients suffering from thyroid cancer (25 papillary carcinomas, 1 follicular carcinoma) using 8 microsatellite markers. Microsatellite instability (MSI) was found in two (7.7%) papillary carcinomas. Our data indicate that MSI is a relatively rare event and may seldom contribute to the carcinogenesis of papillary carcinomas of the thyroid.