Calcaneus tendons and ankles of 25 practising marathon runners were investigated by sonography and MR. We applied a 7.5 MHz transducer for sonography. Axial and sagittal T1-weighted, proton density-weighted, and T2-weighted SE images were performed. MR proved superior to sonography. Degenerative alterations of the calcaneus tendon, tendovaginitis of the flexor hallucis longus muscle, joint effusions and cartilage disease were diagnosed by MR but remained undetected by sonography.