Male patients with type 2 diabetes mellitus (DM) may experience infertility because the disease affects negatively many aspects of reproduction, including seminal vesicle (SV) function. The aim of this study was to evaluate the ultrasound characteristics of the SVs of infertile patients with DM because no such data are available in these patients. To accomplish this, 25 infertile patients with type 2 DM and no other known causes of sperm parameter abnormalities were selected. Two different control groups were also enrolled: healthy men with idiopathic infertility (n=25) and infertile patients with male accessory gland infections (MAGI) (n=25), a well-studied clinical model of SV inflammation. Patients and controls underwent prostate-vesicular transrectal ultrasonography after 1 day of sexual abstinence before and 1h after ejaculation. The following SV ultrasound parameters were recorded: (1) body antero-posterior diameter (ADP); (2) fundus APD; (3) parietal thickness of the right and left SVs; (4) number of polycyclic areas within both SVs; (5) fundus/body ratio; (6) difference of the parietal thickness between the right and the left SV; and (7) pre- and post-ejaculatory APD difference. Patients with DM had a significantly (p<0.05) higher F/B ratio compared to controls and patients with MAGI. Only patients with MAGI had a significantly (p<0.05) higher number of polycyclic areas. Controls and MAGI patients have a similar pre- and post-ejaculatory difference of the body SV APD, whereas this difference was significantly (p<0.05) lower in patients with DM. In conclusion, this study showed that infertile patients with DM have peculiar SV ultrasound features suggestive of functional atony.