The measurement of the peak exhaled breath temperature (EBT) during multiple tidal breaths offers an easy, non-invasive tool for monitoring airway inflammation. Chronic obstructive pulmonary disease (COPD) is linked to airway inflammation, which is further aggravated by exacerbations of the disease. However, the peak EBT has not been studied in patients with COPD. The breath temperature was measured (X-halo, Delmedica Investments) in 19 control non-smoking subjects (age: 28 ± 11 years, mean ± standard deviation), 19 control smoking/ex-smoking subjects (53 ± 9 years), 20 patients with stable COPD (66 ± 8 years), and 17 patients with COPD at onset and also after recovery from an acute exacerbation (AECOPD; 65 ± 10 years). Spontaneous sputa were collected in AECOPD. The intra-class correlation coefficient of the repeated EBT measurements in non-smokers was 0.87 (95% confidence interval: 0.70-0.95). The peak EBT was different between the subject groups (Kruskal-Wallis test, p = 0.02), with lower values in the patients with stable COPD (34.00/33.35-34.34/°C; median /interquartile range/) than in the smoking/ex-smoking control subjects (34.51/34.20-34.68/°C, p < 0.05). The EBT was higher at the onset of AECOPD (34.58/34.12-34.99/°C, p < 0.05) compared to in a stable condition, and positively correlated with the sputum leukocyte count (p = 0.049, r2 = 0.30; Spearman test) and neutrophil percentage (p = 0.03, r(2) = 0.36). The breath temperature decreased after recovery from AECOPD (34.10/33.72-34.43/°C, p = 0.008; Wilcoxon test). The peak exhaled breath temperature, recorded during multiple tidal breaths, increases with an acute exacerbation of COPD, and may be related to accelerated airway inflammation. The application of exhaled breath temperature measurements when monitoring the activity of COPD should be further assessed in longitudinal studies.