SummaryObjective  Active acromegaly is associated with increased mortality from cardiovascular causes. Several studies have shown increased atherogenic risk factors and biomarkers of inflammation and atherosclerosis in association with growth hormone excess. The aim of this study was to evaluate oxidized low density lipoprotein (oxLDL) levels and some modulators of LDL oxidative modification in patients with acromegaly.Design  Open transversal study.Patients  Fifteen patients with active acromegaly and 15 controls were studied.Measurements  We evaluated the levels of oxLDL, thiobarbituric acid reactive substances (TBARS), ceruloplasmin, bilirubin, uric acid and total reactive antioxidant potential, and the activities of ceruloplasmin, myeloperoxidase, superoxide distmutase, paraoxonase 1, and platelet activating factor acethylhydrolase. Statistical analysis was performed including body mass index as a covariate or as a fixed variable.Results  Patients with acromegaly showed significantly higher levels of oxLDL (120 ± 19 vs. 86 ± 20 U/l, P < 0·001) and endothelin (P < 0·05), increased ceruloplasmin activity (P < 0·01) and a trend towards higher values in TBARS concentration (P = 0·07) in comparison to healthy controls. OxLDL was positively associated with GH, IGF‐I and its binding protein 3 (r = 0·63, P < 0·001; r = 0·53, P < 0·01; and r = 0·56, P < 0·01; respectively). OxLDL showed direct associations with endothelin‐1 (r = 0·53, P < 0·01) and ceruloplasmin activity (r = 0·43, P < 0·05). The other parameters evaluated were similar in both groups.Conclusions  The increase in plasma oxLDL levels, a direct marker of the plaque formation, could constitute a link between atherosclerosis and active acromegaly. LDL oxidation would not be the consequence of diminished antioxidant defences, but of an enhancement in prooxidant factors like ceruloplasmin.