OBJECTIVE: At present, blood and skin biopsy tissues are used in the fluorescent in situ hybridization (FISH) test for the diagnosis of Down's syndrome, however, the samples are usually obtained invasively. This study explores the value of oral mucosa cast-off cells in the FISH test, as samples obtained non-invasively, for the diagnosis of this disorder. METHODS: Peripheral blood and oral mucosa cast-off cells were sampled for the FISH test in 16 children with suspected Down's syndrome between March 2010 and March 2011. Chromosomal karyotype analysis of peripheral blood lymphocytes ("gold standard" for the diagnosis of Down's syndrome) was also conducted. RESULTS: The FISH test, in which both peripheral blood and oral mucosa cast-off cells were examined, showed that 14 children had 21-trosomy syndrome and the other 2 children had normal numbers of cromosome 21. The results of the FISH test were the same as the results of the chromosomal karyotype analysis. CONCLUSIONS: Use of the FISH method to test samples of oral musoca cast-off cells is non-invasive and reliable for the diagnosis of Down's syndrome in children, and is hence worthy of recommendation.