Insulin resistance is a common underlying physiologic abnormality associated with central obesity, type 2 diabetes and cardiovascular disease. Clinically, its hallmark markers of hypertension, glucose intolerance and dyslipidemia have been grouped into associated syndromes of insulin resistance. Insulin resistance is now considered a useful marker of clinical risk and a target for therapeutic intervention. While the criteria for diagnosis of syndromes related to insulin resistance have been established, the clinical diagnosis of insulin resistance remains a significant challenge. As more clinicians focus on the management of insulin resistance in patients with cardiovascular disease, type 2 diabetes and other syndromes of insulin resistance, its diagnosis will take on increasing importance. This review focuses on the current definition and diagnosis of insulin resistance and associated syndromes.