It has been hypothesized that in individuals with diabetes mellitus the peripheral nerve is swollen owing to increased water content related to increased aldose reductase conversion of glucose to sorbitol. It has further been hypothesized that the tibial nerve in the tarsal tunnel is at risk for chronic nerve compression related to this swelling. We used diagnostic ultrasound to evaluate this hypothesis. Cross-sectional areas of the tibial nerve were measured in diabetic patients with neuropathy and compared with previously reported measurements in nondiabetic patients and diabetic patients without neuropathy. We used the Pressure-Specified Sensory Device (Sensory Management Services LLC, Baltimore, Maryland) to document the presence of neuropathy in 24 diabetic patients (48 limbs). Previous studies have found that the cross-sectional area of the tibial nerve in nondiabetic patients and in diabetic patients without neuropathy is not significantly different. We found that the mean cross-sectional area of the tibial nerve in diabetic patients with neuropathy is significantly greater than that in diabetic patients without neuropathy (24.0 versus 12.0 mm(2)). Our study highlights the value of newer ultrasound imaging techniques in identifying morphological change in the tibial nerve and confirms that the tibial nerve in the tarsal tunnel is swollen, consistent with chronic compression, in diabetic patients with neuropathy.