The aim of this pictorial essay was to demonstrate the diagnostic efficacy of high-resolution sonography in detecting bone erosions in a patient with rheumatoid arthritis. Standard X-Ray of the feet did not reveal clearly evident erosions. Ultrasonography was able to detect the presence of bone erosions of the metatarsal heads of both the first toes and of the V toe of the left foot. Because the appearance of bone erosions on radiographs of a patient with a recent onset arthritis indicates a poor prognosis, the possibility of demonstrating small hidden erosions at the level of the early targets of the disease is of relevant practical value.