The purpose of this study was to describe the MR findings of posterior tibial tendon dysfunction.MR images and medical records were reviewed for 11 patients with surgically proven posterior tibial tendon abnormalities (i.e., tears or tenosynovitis) and for six patients with clinical evidence of posterior tibial tendon dysfunction. Our study group included 16 women and one man from 37 to 70 years old (mean, 53.5 years old). MR examinations used T1-weighted and T2-weighted spin-echo sequences in the oblique axial and sagittal planes.Abnormal MR findings were observed in all 17 patients. The spectrum of MR abnormalities included fluid in the tendon sheath of a normal tendon interpreted as isolated paratenonitis (tenosynovitis, n = 3); tendon thickening and surrounding fluid with normal tendon signal interpreted as tendinosis (degeneration, n = 1); tendon thickening with increased linear or heterogeneous intrasubstance signal interpreted as partial tear (n = 11); tendon discontinuity with fluid-filled tendon ...