Aim To determine the prevalence of glaucoma in patients with obstructive sleep apnoea. Design Cross-sectional case series. Participants One hundred patients with moderate to severe obstructive sleep apnoea.Testing Within 48 h of the polysomnographic diagnosis of obstructive sleep apnoea, patients underwent the following tests: intraocular pressure, gonioscopy, automated perimetry, stereoscopic biomicroscopy, and fundascopic assessment for the presence of glaucomatous optic nerve changes. Main outcome measures The prevalence of glaucoma in patients with obstructive sleep apnoea and the associations between patient characteristics and both glaucoma and intraocular pressure. Results Glaucoma was diagnosed in 27 of 100 patients yielding an estimated prevalence of 27% (95% CI 19-37%). The presence of glaucoma did not correlate with sex, body mass index (BMI), or AHI, but did appear to be associated with age (P ¼ 0.014). There was no evidence of a relationship between intraocular pressure and either the apnoea plus hypopnoea index or age. Conclusion The prevalence of glaucoma in patients with obstructive sleep apnoea is an estimated 27%. Sex, age, body mass index or apnoea plus hypopnoea index are not factors influencing the presence of glaucoma in this population of patients.