Purpose. To compare the longitudinal effects of treatment on intraocular pressure (IOP) and visual field performance in Japanese normal tension glaucoma (NTG) between latanoprost and timolol. Pati ents and methods. This is an open label, randomized, study. A total of 62 NTG p atients were prospectively, consecutively enrolled. All study subjects were rand omly assigned to 0.005%latanoprost instillation once daily in the morning or 0. 5%timolol instillation twice daily for a prospective 3 year follow up, and un derwent a routine ocular examination every month. Automated perimetry was perfor med every 6 months using Humphrey field analysers. Stereophotographs of optic di scs were also obtained every 6 months. Results. Percentage of IOP reduction or t he magnitude of IOP reduction showed no intergroup differences either at any tim e point (13-15%). In the visual field, the estimated rate of change in the MD value (dB/year) was-0.34±0.17 (SE) for the latanoprost group, and-0.10±0.18 (SE) for the timolol group. The estimated rate of change in MD showed no signifi cant difference fromzero in both groups, and there were no statistical intergroup differences. No changes in the optic nerve head topography in the vertical cup to disc ratio and rim area measured by imageanalysis techniques were observed in either group. There were no patient s who dropped out due to the side effects of treatment regimens. Conclusion. Bot h latanoprost and timolol single treatments reduced IOP by 13-15%at their trou gh effects for 3 years in Japanese NTG patients; both showed similar effects on visual field performance. To compare the longitudinal effects of treatment on intraocular pressure (IOP) and visual field performance in Japanese normal tension glaucoma (NTG) between latanoprost and timolol. Pati ents and methods. This is an open label, randomized, study. A total of 62 NTG p atients were prospectively, consecutively enrolled. All study subjects were rand omly assigned to 0.005% latanoprost instillation once daily in the morning or 0.5% timolol instillation twice daily for a prospective 3 year follow up, and un derwent a routine ocular Automated perimetry was perfor med every 6 months using Humphrey field analyzers. Stereophotographs of optic di scs were also obtained every 6 months. Results. Percentage of IOP reduction or he magnitude of IOP reduction showed no intergroup differences either at any tim The estimated rate of change in the MD value (dB / year) was-0.34 ± 0.17 (SE) for the latanoprost group, and-0.10 ± 0.18 (SE) for the timolol group. The estimated rate of change in MD showed no signifi cant difference fromzero in both groups, and there were no statistical intergroup differences. No changes in the optic nerve head topography in the vertical cup to disc ratio and rim area measured by There were no patient s who dropped out due to the side effects of treatment regimens. Conclusion. Bot h latanoprost and timolol single treatment reduced IOP by 13-15% at their trou gh effects for 3 years in Japanese NTG patients; both have similar effects on visual field performance.