There is still no consensus on a normal value for the cross-sectional area of the ulnar nerve at the elbow. Such data would be valuable for the ultrasound diagnosis of ulnar neuropathy. Comparison of the symptomatic and contralateral asymptomatic sides has been recommended. The aim of this study was to investigate whether or not the asymptomatic ulnar nerve could be a reference value. High-resolution ultrasonic measurements of the cross-sectional areas of the ulnar nerves at the elbow were compared with 38 contralateral asymptomatic elbows of patients with unilateral ulnar neuropathy and 38 healthy controls. There were significant differences in the cross-sectional areas at all levels between the healthy control subjects and asymptomatic side of the ulnar neuropathy patients (p < 0.05). The findings of this study suggest that there is a limitation in using the asymptomatic side for obtaining reference values in ultrasonographic studies. Each ultrasonographic laboratory should determine its own reference values.