Using fluorescence in situ hybridization, we have detected trisomy 3 and the frequency of cells with +3 in 36 patients with AILD. In 36 cases 28 (77.8%) were found having trisomy 3, which was far exceeded that observed in metaphase cytogenetic study (+3 in 15 cases, 42%). Meanwhile, the frequency of cells with +3 was only 4.0%, which was much lower than that of 11.2% in metaphase cytogenetics. The study indicate that the trisomy 3 is a characteristic chromosome aberration of AILD, the cells with +3 constitute only a small part of the specimen, the fluorescence in situ hybridization is more sensitive than metaphase cytogenetics in detection of numerical chromosome aberrations.