The MTA1 gene is a recently identified metastasis-associated gene which has been implicated in the signal transduction or regulation of gene expression. We examined the mRNA expression levels of the MTA1, the human homologue of the rat mta1 gene in thymoma. Expression of MTA1 mRNA was evaluated by reverse transcription polymerase chain reaction (RT-PCR) in 30 thymoma samples using LightCycler. The data was analyzed in reference to clinicopathological data. There was no relationship between MTA1 gene expression and age and gender. MTA1/GAPDH mRNA level in stage IV thymoma (6.431+/-3.404) was significantly higher than the level in stage I thymoma (2.592+/-1.902, P=0.0081). There was a tendency towards higher MTA1/GAPDH mRNA level in stage IV thymoma when compared to stage II thymoma (3.746+/-3.292, P=0.072). Thus our results show that the expression of the MTA1 gene is closely related to invasiveness in thymoma. The gene MTA1 could potentially provide information on the mechanism of tumor invasion and metastasis.