BACKGROUND: Studies have supported the correlation between mean platelet volume and COPD. However, there are limited data on the relationship between COPD exacerbation and mean platelet volume. We aimed to evaluate the mean platelet volume trend in patients with COPD exacerbation. METHODS: A total of 81 subjects, 62 men and 19 women, who were admitted to the hospital because of exacerbation of COPD during 9 months, were enrolled in this prospective observational study. The levels of mean platelet volume, C-reactive protein, complete blood count, and percentof-predicted FEV 1 were measured in subjects at admission (exacerbation period) and after 3 months (stable period). Thirty-seven age-and sex-matched healthy individuals constituted the control group. RESULTS: Subjects in the exacerbation period had significantly higher levels of C-reactive protein (P ‫؍‬ .001), white blood cell count (P ‫؍‬ .01), and percentage of neutrophils (P ‫؍‬ .01) and lower percent-of-predicted FEV 1 than in the stable period (P ‫؍‬ .02). Mean platelet volume levels were significantly decreased in the exacerbation period (P ‫؍‬ .001). Considering a cut-off point of mean platelet volume levels <8.2 fL for indicating COPD exacerbation showed a sensitivity of 80% and a specificity of 76%. Also, mean platelet volume levels correlated significantly with increase of C-reactive protein level, white blood cell count, and neutrophil percentage in the exacerbation period (P ‫؍‬ .01, P ‫؍‬ .01, and P ‫؍‬ .02, respectively). CONCLUSIONS: Mean platelet volume may be an inflammatory marker in exacerbation of COPD, and the measurement of mean platelet volume values may be useful for identifying patients who are at increased risk for exacerbations of illness.