The pretibial area is the most frequently affected site in necrobiosis lipoidica (NL), but proposed mechanisms of NL cannot fully explain this high frequency. Although a few case reports indicate NL patients are complicated with venous insufficiency, no accurate assessment of the relationship between these two conditions has been performed. By using color Doppler ultrasonographic screening of four NL patients for venous insufficiency, we detected venous insufficiency in at least one leg of each patient. NL lesions were observed on all legs with venous insufficiency, and laboratory examination findings revealed that all the patients had hypercholesterolemia. The skin lesions did not respond satisfactorily to 6-month use of anticholesterolemic medication and elastic stockings. However, these results indicate that both hyperlipidemia and venous reflux, in addition to other pathogenic factors, can trigger tissue damage in the lower legs and lead to the onset of NL.