The recent improvement of musculoskeletal imaging achieved by high-frequency ultrasonography (US) and its important advantages as a routine dynamic imaging tool-providing results rapidly, absence of secondary effects, and low cost-make US a very useful tool in rheumatologic practice. We prospectively compared high-frequency US with magnetic resonance imaging (MRI) in patients with painful shoulder syndrome.Thirty-four consecutive patients (36 shoulders) with a first flare of shoulder pain were included in the study. US and MRI shoulder examination were performed within 2 weeks. US shoulder examinations were performed by a rheumatologist experienced in US, without knowledge of the MRI results. The MRI results were considered the gold standard. US showed high sensitivity, specificity, and positive and negative predictive values (range 85.7%-100%) in the diagnosis of tendinitis, partial-thickness, and full-thickness tear of the rotator cuff and degenerative changes of the acromio-clavicular joint. Rotator cuff calcifications were detected only by US. We highly recommend that for many painful shoulders, appropriately trained rheumatologists can perform US examinations to establish an accurate diagnosis and, thereby, improve therapy.