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Adipose tissue (AT)-thyrocyte interaction is largely unknown. Here we described the interaction in a co-culture system, in which thyrocytes were cultured on AT fragment (ATF)-embedded collagen gel, using electron microscopy, immunocytochemistry, real-time reverse transcription–polymerase chain reaction (RT–PCR) and enzyme-linked immunosorbent assay (ELISA). ATFs promoted the hypertrophy, polarization and lipid accumulation of thyrocytes. ATFs did not affect the growth of thyroyctes, and inhibited their apoptosis. ATFs increased the protein expression of thyroglobulin (Tg) and paired box gene 8 (PAX8) in thyrocytes. In turn, thyrocytes decreased the concentration of leptin and adiponectin, and increased the expression of these mRNAs in ATFs. Thyrotropin (TSH) enhanced the ATF-induced nuclear hypertrophy and Tg protein expression in thyrocytes, while TSH enhanced the thyrocyte-induced expression of leptin and adiponectin mRNAs in ATFs. Finally, leptin promoted the hypertrophy and Tg protein expression in thyrocytes. TSH enhanced these leptin-induced effects. The data indicate an active interaction between thyrocytes and AT, suggesting that (i) ATFs may serve to regulate the morphology, survival and differentiation of thyrocytes probably through lipid accumulation partly in a TSH-synergistic way; (ii) thyrocytes may affect adipokine production from ATFs in a TSH-independent manner; and (3) leptin may be related to the hypertrophy and differentiation of thyrocytes in a TSH-synergistic way.