Adult adipose-derived stem cells (ASCs) are considered to be an alternative cell source for cell-based cartilage repair because of their multiple differentiation potentials. This article addresses the chondrogenic differentiation of ASCs seeded into poly-lactide-co-glycolide (PLGA) scaffolds after implantation in a subcutaneous pocket of nude mice. Human ASCs were seeded into PLGA (polylactic acid:polyglycolic acid = 90:10) scaffolds and cultured in transforming growth factor beta 1 (TGF-beta1)-containing medium for 3 weeks in vitro. Then specimens were implanted into a subcutaneous pocket of severe combined immunodeficiency mice and harvested after 8 weeks. Chondrospecific messenger RNA (mRNA) expression was analyzed using reverse transcriptase polymerase chain reaction. Corresponding extracellular matrix (ECM) synthesis was demonstrated using immunohistochemical staining. Chondrospecific marker molecules such as collagen type II and type X, cartilage oligomeric matrix protein, and aggrecan subsequently increased during the 3 weeks period in vitro. After a further 8 weeks, in vivo samples pretreated with TGF-beta1 continued expressing collagen type II and aggrecan mRNA, and collagen type II was found within the ECM using immunohistochemistry. Chondrospecific mRNA was not detected in control samples. ASC-seeded PLGA scaffolds express a stable chondrogenic phenotype in a heterotopic model of cartilage transplantation and represent a suitable tool for tissue engineering of cartilage.