The analysis conducted in this study regarding the relationship between tenascin C and adiponectin concentrations in the blood of children with juvenile idiopathic arthritis during successive months of etanercept therapy—specifically in the third (R = 0.016; p > 0.05), sixth (R = −0.065; p > 0.05), twelfth (R = −0.061; p > 0.05), and eighteenth (R = −0.216; p > 0.05) months—did not reveal any significant associations between these parameters. The gene discussed is TNC; the disease is juvenile idiopathic arthritis.