The FHIT gene is located at 3p14.2 a region frequently lost in multiple tumour types. Loss of FHIT expression has been found to occur frequently in multiple tumour types. We wished to investigate that FHIT mRNA levels in a series of thymomas.Expression of FHIT messenger ribonucleic acid (RNA) was evaluated by reverse transcription-polymerase chain reaction (RT-PCR) using a LightCycler in 49 thymomas and 11 adjacent histologically normal thymus samples from patients.FHIT transcripts in tumour samples (28.6+/-35.8) at levels significantly lower than those in normal thymus samples (573.9+/-1028.0, p=0.001). No relationship was seen between FHIT gene expression and age, gender, or pathological thymoma subtypes. FHIT mRNA expression in invasive thymomas (stage II-IV, 34.5+/-39.2) was significantly higher than that in stage I thymomas (20.7+/-29.7, p=0.01). Immunohistochemistry showed that p21 protein positive thymoma had a tendency towards higher FHIT gene expression than in p21 negative thymoma.Decreased FHIT expression might be seen in early stage thymoma, suggesting that loss of FHIT expression may associate with tumorigenesis of thymoma.