To investigate the effect of diabetes mellitus on the Achilles tendon, which may contribute to the long-term complications in the foot-ankle complex and to investigate the factors relating to its thickening. The study group included 55 patients (26 female and 29 male) with type 2 DM, while the control group included 34 non-diabetic people (13 female and 21 male). We matched the female and male DM patients with their respective control groups in terms of age, BMI, height and body weight. Clinical and biochemical tests, as well as ultrasonographic evaluations of the internal carotid artery and the Achilles tendon, were carried out to evaluate the complications of diabetes mellitus, and to compare the Achilles tendon thickness (ATT) between the study and the control groups. In the female groups the Achilles tendon was significantly thicker in the diabetic patients than in their healthy controls (p<0.001). However, no difference was found in the ATT between the male diabetic patients and their male controls (p=0.74). The ATT correlated with the body mass index (BMI) (r=0.47, p=0.015) and body weight in diabetic female group (r=0.56, p=0.003). We also observed that the ATT values were higher in male DM patients with retinopathy (p=0.034) or neuropathy (p=0.019) compared to the male DM patients without these complications. The ATT in type 2 female diabetic patients was found to be higher than their non-diabetic controls, but no significant difference could be found between type 2 diabetic male patients and their non-diabetic controls by US. Our results might indicate a possible impact of diabetes on the ATT depending upon gender, but other mechanisms may also contribute to thickening of Achilles tendon.