To study plasma copeptin (the stable portion of vasopressin molecule) as a marker for predicting frequency, severity and need for hospital admission in COPD patients; we followed up 50 patients with moderate severity (GOLD 2007, stage II) for one year. Their plasma copeptin levels were measured at the beginning, during first and last exacerbations as well as one month post exacerbations. 20 age matched healthy subjects (10 smokers and 10 non smokers) were also studied as controls. We found significantly higher copeptin levels in patients than controls while no significant difference was seen between smoker and non smoker controls (p < 0.001, p > 0.05 respectively). Copeptin levels were significantly elevated during exacerbations than basal pre-exacerbation levels and at all testing times, admitted patients had significantly higher levels than non admitted (p< 0.001 for all). In patients needed admission for more than a week copeptin levels were significantly higher than in those admitted for less than a week ( p