Background: Functional and morphological changes of endothelium were risk factors for mortality attributed to atherosclerosis. Studies investigating early atherosclerotic alterations and the effect of the treatment of acromegaly on these alterations gave conflicting results. Objective: Surrogate markers of early atherosclerotic changes, i.e. brachial artery flow-mediated dilation (FMD) and carotid artery intima-media-thickness (IMT) in active and inactive acromegalic patients were compared with control subjects matched to patients for age, sex and cardiovascular risk factors to find out the direct effects of growth hormone (GH)/insulin-like growth factor-1 excess. Methods: In 14 active acromegalics and their 14 matched controls, 14 inactive acromegalics and their 14 matched controls, carotid artery IMT and FMD of brachial artery were measured. Inactive acromegalics were in remission for at least 1 year. Results: Active acromegalics had higher IMT than matched controls and inactive acromegalics (0.85 +/- 0.20 mm, 0.64 +/- 1.77 mm, 0.66 +/- 0.20 mm respectively; p < 0.005, p < 0.05) and IMT of inactive acromegalics was not different from their matched controls (0.61 +/- 0.12 mm). FMD was significantly lower in active acromegalics than in matched controls and inactive acromegalics (2.910 +/- 2.00 mm, 6.5 +/- 2.81 mm, 5.68 +/- 2.9 mm respectively; p < 0.005, p < 0.05). FMD of inactive acromegalics was not significantly different from their matched controls (7.96 +/- 3.12 mm). A significant inverse relationship was found between GH and FMD in active acromegalics (r = -0.659, p = 0.010). Conclusion: In active acromegalics, early atherosclerotic changes are not only attributed to the high prevalence of risk factors, but also to the abnormal GH secretion itself.