Purpose The aim of this study was to evaluate the 24-h intraocular pressure (IOP) fluctuations in patients with glaucoma and to compare them with normal persons.Patients and methods This is a cross-sectional comparative study of the circadian rhythm of IOP that was conducted on 30 patients diagnosed with primary glaucoma on medical or surgical treatment and 30 normal individuals with no signs of glaucoma. There were three cases of primary angle closure glaucoma, and so they were excluded from the analysis.Results The mean age of all participants was 60.25±12.15 years. The mean age of the normal individuals was 58.60±12.33 years compared with 62.22±11.66 years in patients with primary open angle glaucoma (POAG), with no statistically significant difference (P=0.486). A higher proportion of females (63%) were found in the glaucoma group, though not statistically significant (P=0.138). The mean IOP was higher among the glaucoma group (19.92±6.18 mmHg) than in the normal individuals (14.83±1.75 mmHg), with a statistically significant difference (P=0.001). The mean diurnal variation of IOP in the right eye among the normal individuals (3.6±1.1 mmHg) was significantly lower than in the POAG group (7.11±4.8 mmHg) (P=0.001). Similarly, in the left eye, the mean diurnal variation was significantly higher in the POAG group (6.07±2.25 mmHg) compared with the normal individuals (3.52±1.25 mmHg) (P=0.00). The average peak of IOP among normal individuals and patients with POAG was 19.75±2.0 and 37.56.9 mmHg, respectively, in the right eye (P=0.01) and 20.00 ± 1.6 mmHg and 26.25 ± 2.2 in normal individuals and patients with POAG, respectively, in the left eye (P=0.001). The peak IOP among the POAG group was seen at 6 p.m. and 6 a.m., mostly outside office hours.Conclusion The diurnal variation of IOP was more among patients with glaucoma than normal individuals. The average peak of the IOP was seen only after office hours (9 a.m.–5 p.m.), thus emphasizing the need for 24-h monitoring of IOP. The 24-h measurement would help recognize the IOP spikes and help decide the time of instillation of antiglaucoma medication to avoid further glaucoma progression.