OBJECTIVE To characterize the circadian pattern of habitual-position intraocular pressure (IOP) and its association with ocular dimension in young myopic patients with open-angle glaucoma (OAG). METHODS A total of 108 young OAG patients with moderate to severe myopia (myopia group) and 67 age-matched OAG patients with emmetropia or mild myopia (control group) were recruited prospectively over 3 years. IOP was recorded 11 times over a 24-hour period by a single, well-trained ophthalmology resident using a handheld tonometer. RESULTS A total of 87 men and 88 women were included in this study. Analysis of the entire myopia group indicated no acrophase in habitual-position IOP over 24 hours. Subgroup analysis indicated that 44 patients (40.7%) had a diurnal acrophase, 17 patients (15.7%) had a nocturnal acrophase, and 47 patients (43.6%) had no evident acrophase. By contrast, the control group showed an overall nocturnal acrophase in habitual-position IOP, with 14 patients (20.8%) having a diurnal acrophase, 30 patients (44.8%) having a nocturnal acrophase, and 23 patients (34.4%) having no evident acrophase in subgroup analysis. There was a negative correlation between nocturnal habitual-position IOP elevation and axial length in the overall population. CONCLUSIONS In young myopic OAG eyes, there is no significant nocturnal elevation in habitual-position IOP, while IOP increases at night-time in age-matched control eyes. The overall 24-hour IOP pattern in the myopia group did not show an acrophase. Finally, data showed a negative relationship between nocturnal habitual-position IOP elevation and axial length.