PURPOSE: To assess the sonographic characteristics of soft tissue tumor and to determine whether color flow Doppler sonography is useful for distinguishing benign from malignant soft tissue masses. MATERIALS AND METHODS: Sixty five soft tissue masses were evaluated with color flow Doppler sonography. The pulsatility index (PI) and resistive index (RI) were calculated from the waveform generated from blood flow within the soft tissue mass. In addition, the size and shape, homogeneity of internal echogenecity and internal necrosis of mass were also evaluated retrospectively. RESULT: Forty two lesions were benign, and 23 were malignant on pathologic examination. Benign lesions included 12 lipomas, 11 hemangiomas, 8 schwannomas, 4 neurofibromas, 4 fibromas, a desmoid tumor, and etc. Malignant lesions consisted of 5 liposarcomas, 3 malignant lymphomas, 2 malignant fibrous histiocytomas, a rhabdomyosarcoma, a malignant schwannoma, a hemangiopericytoma, a dermatofibrosarcoma, a synovial sarcoma, 4 metastatic tumors and etc. Twenty seven benign and 17 malignant lesions showed color flow signals and spectral waves on Doppler sonography. Mean PI, RI of benign and malignant tumors were 0.9381+/-0.2935, 0.5988+/-0.1339 and 0.8383+/-0.1795, 0.5772+/- 0.0871, respectively (p> 0.05). Hemangiomas had a lower PI and RI (mean, 0.7446+/-0.3253, 0.4973+/-0.1351) than the others of benign tumors (PI: mean 1.0190+/-0.2175, RI: mean 0.6285 > 0.1038) (p=0.115, 0.027). Mean size of benign and malignant tumor was 3,21+/-0.98cm and 5.27+/-2.59cm, respectively. Eighty three percent (35/42) of benign and 26% (6/23) of malignant masses showed smooth margin. The homogeneity of internal echoes were shown in 55% (23/42) of benign, and 30% (7/23) of malignant masses, respectively. Fifty seven percent (13/23) of malignant masses showed intratumoral necrosis, whereas benign masses showed in 7% (3/42). CONCLUSION: The pulsatility index and resistive index tend to be lower in malignant masses, but neither is significant statistically. The intratumoral necrosis and marginal irregularity are helpful in differentiation of malignant from benign masses.