The sensitivity of tissue to insulin is of physiological, pathophysiological and therapeutic relevance. The quantity of insulin and the response to insulin are paramount complementary factors in the regulation of glucose metabolism, and may, at least under certain pathophysiological conditions, also affect cardiovascular function. Hypertension has a high prevalence among subjects with decreased insulin sensitivity and/or hyperinsulinaemia due to obesity, impaired glucose tolerance, non-insulin-dependent diabetes mellitus, and certain other conditions. There is evidence that, even in the absence of obesity or diabetes mellitus, essential hypertension tends to be associated with insulin resistance. The latter elicits a compensatory increase in insulin secretion. Hyperinsulinaemia also occurs in diabetes type 1 as a consequence of insulin treatment. Considering the acute effects of insulin on sympathetic nervous activity, transmembranous cation transport, renal sodium reabsorption, cellular proliferation and lipid metabolism, insulin resistance and/or hyperinsulinaemia may possibly contribute to the genesis of essential, obesity-associated and diabetes-associated hypertension, and may also promote dyslipidaemia in these disorders.