Pulmonary hypertension has been recognized as being associated with obstructive sleep apnoea (OSA). Continuous positive airway pressure (CPAP) might reduce pulmonary artery pressure in OSA patients; however, evidence from clinical studies is limited and inconsistent. This meta-analysis aims to assess whether CPAP is associated with a decrease in pulmonary artery pressure in patients with OSA. This systematic review was performed in accordance with the Meta-analysis of Observational Studies in Epidemiology guidelines. Published studies were identified through a search in MEDLINE, EMBASE and the Cochrane library through to May 2013. Two reviewers sorted papers and extracted data. A random-effects model was used to combine results across studies comparing pulmonary artery pressure in OSA patients before and after CPAP treatment. Six articles with 181 patients were included in this meta-analysis, including five before-after studies and one matched-control study. The meta-analysis showed that CPAP was associated with a statistically significant reduction in pulmonary artery pressure in OSA patients (standardized mean difference −1.34, 95% confidence interval: −2.33 to −0.34, P = 0.009). Although this meta-analysis has some limitations, it indicates that CPAP is associated with a decrease in pulmonary artery pressure in patients with OSA.