Ultrasound (US) should be considered an integral part of the imaging arsenal of the musculoskeletal radiologist. It offers many advantages over other imaging modalities of which, the contact between the radiologist and the patient at the time of examination and its dynamic imaging capabilities are unique. Coupled with color Doppler it gives important information on the vascularity of soft-tissue masses, and it provides rapid, real-time guidance for fine-needle aspiration and biopsy. This article discusses the role of US in the diagnosis of soft-tissue masses. We also propose an algorithm for the investigation of a patient with a suspected soft-tissue mass which uses US and Doppler studies as the second-line imaging modality after radiographs. US is helpful in the diagnosis of cystic and solid soft-tissue masses but, as with any other imaging studies, it is important to know its limitations. Sometimes MRI should be done in place of, or to complement the US examination. In many cases, a biopsy is needed to arrive at a precise and final diagnosis.