Objective: To investigate the effect of hospitalization on intraocular pressure (IOP) in patients with normal-tension glaucoma (NTG). Methods: The study was conducted in 52 patients with a definite diagnosis of NTG. The correlation between IOP measured from 9.00 a.m. to 12.00 p.m. on an outpatient basis within 3 months each prior to and after hospitalization (ambulatory IOP) and IOP measured during the same time period after admission (inpatient IOP) was investigated in NTG patients. Results: Inpatient IOP (13.9 ± 2.4 mm Hg) was significantly lower than ambulatory IOP (15.2 ± 2.1 mm Hg), with a difference of 1.3 ± 2.0 mm Hg (p < 0.01). The difference between inpatient IOP and ambulatory IOP was negatively correlated with inpatient IOP (r = 0.58, p < 0.01). Conclusions: These results revealed that hospitalization decreased IOP in NTG patients, with the decrease being particularly pronounced in cases of low ambulatory IOP. Interpretation of inpatient IOP should be carefully included in glaucoma treatment.