Background: The prevalence and the prognostic impact of chronic obstructive pulmonary disease (COPD) and asthma in patients with myeloproliferative neoplasms (MPNs) are unknown. Methods: This retrospective multicenter cohort analyzed the prevalence and prognostic implications of COPD and asthma in 246 patients with essential thrombocythemia (ET) and polycythemia vera (PV). Results: A total of 6.5% and 1.6% patients had COPD or asthma, respectively, without statistically significant differences with respect to disease phenotype. The presence of COPD/asthma was more frequently associated with active/prior smoking (p = 0.021) and constitutional symptoms (p = 0.001). After the median follow-up of 47.5 months, the presence of COPD/asthma was univariately associated with an inferior time to thrombosis (TTT; median 135 vs. 190 months, 95% confidence interval (CI) 1.8–29.5, hazard ratio-HR 7.75, p = 0.005), mainly driven by venous (HR 37.3, 95% CI 3.2–43.6, p = 0.003) and not arterial events (HR 1.77, 95% CI 0.40–7.78, p = 0.445, p = 0.445). Statistically significant interactions existed between COPD/asthma, female sex (HR 3.94, 95% CI 1.01–11.02), ET phenotype (HR 7.1, 95% CI 15.3–16.7), JAK2 positive status (HR 4.17, 95% CI 1.04–6.9), hydroxyurea use (HR 4.67, 95% CI 1.10–7.43), and the presence of other cardiovascular risk factors (HR 8.1, 95% CI 1.55–10.72) with overall thrombotic risk (interaction p < 0.050 for all analyses). Finally, the negative effect of COPD/asthma on TTT persisted in the multivariate analysis (HR 6.54, p = 0.010) independently of older (>60 years) age (p = 0.030) when being adjusted for other clinically meaningful variables. There was no effect of COPD/asthma on overall survival. Conclusions: These results provide an important signal regarding the potentially inferior outcomes in ET/PV patients presenting with these common respiratory disorders and may help to further personalize MPN management.