Aim: To explore the association of plasma copeptin, the C-terminal portion of provasopressin and a stable surrogate marker for arginine vasopressin secretion, with plasma glucagon in obese men and men of normal weight. Methods: We measured fasting blood concentrations of copeptin and glucagon in 102 healthy obese men (mean ± sd age 49.4 ± 10.2 years) and a control group 27 healthy men of normal weight (mean ± sd age 51.5 ± 8.4 years). Differences between groups were evaluated using t-tests, and multiple linear regression analysis, adjusting for age and weight status (normal weight vs obese), was used to calculate unstandardized regression coefficients (β) with 95% CIs between copeptin and glucagon. Copeptin was (natural) log-transformed. Results: The obese men had higher [median (interquartile range)] plasma copeptin concentrations [6.6 (4.6–9.5) vs 4.9 (3.5–6.8) pmol/l; P = 0.040] and higher mean ± sd plasma glucagon concentrations (8.5 ± 3.8 vs 5.3 ± 1.4 pmol/l; P < 0.001) than the normal-weight men. Adjusted for age and weight status, copeptin was significantly associated with glucagon (β = 1.35, 95% CI 0.13–2.57; P = 0.031). No significant interaction effect between copeptin and weight status on glucagon was found (P = 0.81). Conclusions: Obese men had higher concentrations of copeptin and glucagon than men of normal weight. Copeptin was positively associated with glucagon. Our data suggest that increased arginine vasopressin-stimulated glucagon secretion might contribute to higher glucagon concentrations; therefore, increased arginine vasopressin secretion, in addition to other factors, could further aggravate the hyperglucagonaemic state found in obese individuals.