Chromosomal translocations encoding fusion oncoproteins are common in hematological malignancies, sarcomas, and papillary thyroid carcinomas. A recent study of follicular thyroid carcinomas reported a novel chromosomal translocation, t(2;3)(q13;p25), that fused the thyroid-specific transcription factor PAX8 with a nuclear receptor, peroxisome proliferator-activated receptor γ (PPARγ). Herein we report the detection of this putative oncoprotein in 6 of 17 (35%) follicular thyroid carcinomas as well as in 6 of 11 (55%) follicular thyroid adenomas. Concordant expression of protein was found in 91% of those tumors in which PAX8-PPARγ mRNA was detected by RT-PCR, whereas a further 20% of follicular tumors were positive for PPARγ immunohistochemistry alone. Our findings suggest that the PAX8-PPARγ fusion protein promotes differentiated follicular thyroid neoplasia, although it is not sufficient per se for carcinogenesis.