Background Ultrasound has been increasingly used for the evaluation of superficial soft tissue lesions. Dermatofibroma is one of the most common dermal lesions. Experiences in ultrasound examinations of dermatofibromas have been accumulated. Purpose To evaluate sonographic findings of dermatofibroma and to correlate them with pathologic findings. Material and Methods A total of 18 dermatofibromas in 15 patients were included. Sonographic findings were assessed for location, depth, size, shape, margin, spiculation, echogenicity, internal hyperechoic dots, change in echogenicity of adjacent soft tissue, and vascularity, by two musculoskeletal radiologists in consensus. Pathologic findings were evaluated by one pathologist. Ultrasonographic characteristics were correlated with the pathologic findings by discussion between one radiologist and one pathologist. Results On ultrasound, all lesions were found to be located in the dermis, and 14 lesions (78%) extended into the subcutaneous layer. Mean size was 7 mm (range = 3 to 10 mm). Characteristic findings were ill-defined margins (n = 15, 83%), spiculated margins (n = 12, 67%), change in echogenicity of adjacent soft tissue (n = 14, 78%), and no Doppler flow (n = 14, 78%). Histologically, depth, margin, and spiculation were correlated with sonographic findings. Reactive fibrosis and chronic inflammation were seen in adjacent dermis and subcutaneous fat layer of echogenicity change. Conclusion On ultrasound, dermatofibromas are usually visible as avascular dermal lesions with extension into the subcutaneous layer, and are characterized by ill-defined margins, marginal spiculation, and change in echogenicity of surrounding soft tissues.