Background: Presentation of skin and soft tissue infections (SSTIs) to the pediatric emergency department (PED) has increased. Physical examination alone can be inadequate in differentiating cellulitis from an abscess. The purposes of this study were to determine the effect of bedside ultrasound (US) in improving diagnostic accuracy for SSTIs in the PED and to evaluate its effect on the management of patients with SSTIs. Methods: We conducted a prospective study of a convenience sample of children who presented to an inner-city PED with signs and symptoms of SSTI. The treating physician's pretest opinions regarding the need for incision and drainage and procedural sedation were collected. A bedside US was performed by trained PED physicians to evaluate for cellulitis vs abscess. The treating physician was made aware of the US findings, and the effect on management was recorded. Results: Sixty-five patients were enrolled, of whom 47 had US-proven abscess and 18 had cellulitis. The sensitivity of US for detection of abscess was 97.5% (95% confidence interval [CI], 90.1%-99.5%), and the specificity was 69.2% (95% CI, 57.8-72.4%). In comparison, the sensitivity for physical examination alone for detection of abscess was 78.7% (95% CI, 71.4%-84.4%), and the specificity was 66.7% (95% CI, 47.6-81.6%). Ultrasound disagreed with clinical examination and changed management in 9 (13.8%) of 65 patients. Conclusions: Emergency department bedside US improves accuracy in diagnosis of SSTIs. Bedside US changes management in a small but significant number of patients with SSTIs.