Elevated serum uric acid (SUA) levels (i.e. hyperuricaemia) have been associated with metabolic syndrome (MetS) and cardiovascular disease (CVD) morbidity and mortality. Elevated SUA levels predict the onset of type 2 diabetes (T2DM). SUA levels are increased during the early stages of impaired glucose metabolism. Furthermore, in diabetic patients, hyperuricaemia has been linked to both micro- and macrovascular complications. The present review considers: (1) SUA levels in patients with MetS, type 1 diabetes and T2DM; (2) the mechanisms that influence SUA levels in these patients; (3) the potential links between SUA and diabetic complications. The effect on SUA levels of drugs commonly prescribed for T2DM and the risk of uric acid nephrolithiasis in patients with MetS or DM are also briefly discussed.