**Abstract**

Individuals with diabetes mellitus (DM) are at high risk of thrombosis in which hyperactive platelets are implicated. The platelet hyperactivity has been linked to hyperglycemia. This hypothesis is supported by studies in type II diabetes mellitus showing increased sensitivity of platelets to stimulating agonists in the context of tissue resistance to high-circulating insulin. However, controversy still exists regarding the altered platelet functions in type 1 diabetes mellitus (T1DM) and the link to modifying factors such as blood glucose, hyperlipidemia, metabolic acidosis and insulin treatment. Moreover, increased insulin dosage or treatment appears to have antagonistic actions: diminished functions at low doses and enhanced activation at high doses, the switch being attributable to insulin-like growth factor. The physiological role of insulin in suppressing platelet activation is lost in T1DM, a scenario that favors increased platelet sensitivity to stimulating agonists. Furthermore, the response to antiplatelet agents and statins is sub-optimal in diabetics presenting clinical and research knowledge gap regarding the ideal antiplatelet treatment in DM in general and T1DM in particular. This chapter reviews the unique characteristics of platelet functions in T1DM highlighting the controversial areas linking unique behavior of platelets and the abnormal response to therapeutic interventions.

**Keywords:** type 1 diabetes mellitus, platelets, hyperactivity, thrombosis, platelet functions
