The aim of the study was to investigate the anatomical distribution, morphological abnormalities and response to Tumor Necrosis Factor-inhibitor (TNF-I) therapy of US-detected peripheral enthesitis lesions in a cohort of patients with axial SpA, with or without symptomatic peripheral enthesitis, initiating adalimumab therapy, applying the OMERACT US definitions for enthesitis lesions. The gene discussed is TNF; the disease is enthesitis.