Diabetes mellitus (DM), a growing health problem itself, is accompanied by an increased risk of cardiovascular and thrombotic complications. The imbalance between coagulation and fibrinolysis processes observed in patients with diabetes may be defined as diabetic thrombophilia. Several mechanisms are involved in the hypercoagulability state in diabetics, including endothelial cell damage, altered platelet structure and function, increased microparticle formation, different structure of fibrin clots, disturbances in the activity of coagulation factors, fluctuations in the concentrations of fibrinolysis activators and inhibitors, and qualitative changes of proteins due to glycation and oxidation processes. These all are the reasons why DM is the most common cause of acquired thrombophilia. Moreover, diabetes changes the efficacy of certain medications. Results of various trials seem to suggest that thrombolytic drugs are less effective in patients suffering from this disease. The impact of DM on the effectiveness of treatment with acetylsalicylic acid (ASA) remains unclear. Awareness of thrombotic complications in diabetic patients may enable earlier diagnosis and proper therapy.