It has recently been reported that mismatch repair enzymes, which are one type of DNA repair enzymes, are the causative genes for a major group of hereditary non-polyposis colon cancers (HNPCC). Abnormalities in the mismatch repair system can be monitored by observing instability at the microsatellite loci (MSI) in cancer cells. MSI has been reported not only in tumors associated with hereditary non-polyposis colorectal cancer but also in sporadic forms of various tumors. No correlation between pediatric malignant tumors and the mismatch repair system has yet been reported. In the present study, we examined the frequency of MSI in 21 neuroblastomas, which are the most common solid tumors in childhood, using a high resolution fluorescent microsatellite analysis. MSI on five microsatellite loci was detected in none of the 21 samples. Other mechanisms independent of mismatch repair deficiency may thus play a role in both tumorigenesis and the development of neuroblastoma.