The lower limbs of 84 consecutive patients (48 women and 36 men, age range: 16-75 years, average: 38 years) suffering from acute aching calf symptoms were examined with conventional and color Doppler US. Thirteen cases of muscular thrombosis in the calf were observed, together with 19 cases of deep venous thrombosis, 7 post-phlebitic syndromes, 9 lymphatic obstructions, 6 muscular hematomas and 7 popliteal articular cysts. Case history, clinical signs and phlebography do not allow the former condition to be differentiated definitely from the latter ones--especially hematomas and Baker's cysts which require different treatment protocols. The authors stress the value of conventional and color Doppler US imaging in the aching calf syndrome for its differential diagnostic capabilities. The other more complicated and expensive radiologic and laboratory techniques should be used in case of negative US findings only.