AIM: To investigate the changes of intraocular pressure (IOP) and associated factors of IOP elevation after 4mg intravitreal injection of triamcinolone acetonide (IVTA) in treatment of macular edema. ·METHODS: The study is prospective, consecutive, and non-comparative interventional case series including 93 eyes with macular edema associated with retinal vein occlusion ( =54 eyes) or diabetic retinopathy ( =39 eyes), which received 4mg IVTA injection. The change in IOP was followed for all cases at pre-operation and 14 days, 1, 2, 3, 4, 5, and 6 months post-operation. Associated factors of IOP elevation were examined regarding baseline IOP, causal disease, age and gender. ·RESULTS: IOP increased significantly ( <0.001) at 14 days 16.02 ± 2.45mmHg after injection and peaked at 18.80 ± 6.20mmHg at 2 months post-injection ( <0.001) from 14.85± 2.55 mmHg preoperatively. An IOP rise to the value higher than 21mmHg was observed in 2 (2.2%) eyes 14 days after injection and which was observed in 14 (15.1%), 18 (19.5%), 9(9.6%), 4(4.3%), 0, and 0 eyes respectively at 1, 2, 3, 4, 5, and 6 months after injection. One eye (1.07%) showed pressure elevation of over 5mmHg than baseline 14 days after injection and IOP peaked to 22mmHg (23.7%) at 2 months after injection. Five (5.3%) eyes had an increase of 10mmHg at 1 month and IOP peaked to 12mmHg (12.9%) at 2 months after injection. The rise in IOP was statistically associated with younger age (correlation coefficient -0.18- -0.29, <0.05), high baseline IOP (correlation coefficient 0.52-0.79, all <0.001), and the presence of diabetes mellitus (correlation coefficient 0.23, <0.001) but independent of gender (correlation coefficient -0.002-0.04, all >0.05). In all eyes, IOP could be lowered to the normal range with topical medication, without development of glaucomatous optic nerve head changes. ·CONCLUSION: Elevated IOP after 4mg IVTA injection is common and patients should be monitored beyond 6 months post-injection. In all the cases, IOP can be normalized by topical medication. Patients with high baseline IOP, diabetic retinopathy, and younger age should be carefully monitored for an elevated IOP.