OBJECTIVE.: Vitamin A derivatives, including all-trans-retinoic acid (ATRA), have a well-established role during skeletal development and limb formation and have been shown to have profound effects on chondrocyte phenotype. The aim of this study was to elucidate the effects of retinoids and components of the retinoid metabolic pathway on chondrocyte phenotype in the tibiofemoral joints of patients with osteoarthritis (OA), to show that the retinoids can have multiple effects relevant to the OA disease process. METHODS.: RESULTS.: CONCLUSION.