Insulin resistance is frequently observed in patients with essential hypertension (EHT), and the renin-angiotensin system (RAS) has been demonstrated to modulate the status of insulin resistance. The aims of present study are to investigate the relationship between systemic RAS and insulin resistance in 82 patients with EHT and compare the impact of RAS to insulin resistance with 10 renovascular hypertension (RVHT) patients who have a highly activated systemic RAS. From patients who were admitted to our hospital, patients with overt diabetes and hypertensives who had secondary HT except RVHT or chronic renal failure were excluded. Plasma renin activity (PRA) was used as an indicator of systemic RAS activity. HOMA-R as an index of insulin resistance and sum of immunoreactive insulin (IRI) during glucose tolerance test (sigmaIRI) and IRI at 120 minutes (IRI120) were used as indices of hyperinsulinemia. In the EHT patients, circulating PRA showed an independent relationship with IRI120 and sigmaIRI after adjusting confounding factors (IRI120: t = 2.70, p = 0.01, sigmaIRI: t = 3.05, p < 0.001). Excluding patients who were taking angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II type 1 receptor blocker (ARBs), the relationship remained in univariate linear regression; after adjustment for confounding factors, PRA showed a tendency to be correlated with sigmaIRI. However, there was no significant relationship between PRA and indices of insulin resistance and hyperinsulinemia in patients with RVHT. In conclusion, the systemic RAS may modulate insulin sensitivity in EHT patients.