Patients with coronary artery disease, with (n = 25) and without (n = 59) type 2 diabetes, who were scheduled to undergo coronary artery bypass grafting were enrolled in this prospective study. The left internal thoracic artery (LITA) was assessed for graft suitability before surgery by trans-thoracic Doppler ultrasonography and during surgery by manual measurement. Significant differences were seen between pre-operative and intra-operative LITA blood flow rates and LITA diameters, and the values of each at the two time points showed significant correlation, suggesting that pre-operative measurements largely related to intra-operative conditions. The pre-operative and intra-operative LITA blood flow rates and LITA diameters were not significantly different between patients with and without type 2 diabetes. Pre-operative LITA blood flow was monophasic in three patients without diabetes and the LITA grafts of these patients were deemed unsuitable for implantation during surgery. It is concluded that type 2 diabetes does not seem to have a negative effect on the suitability of LITA grafts. In addition, trans-thoracic Doppler ultrasonography is an easy, cost-effective, reproducible and non-invasive examination method, which may help in the evaluation of LIMA function and contribute to graft selection.