The aim of the present prospective masked study was to assess the effect of bimatoprost monotherapy on ocular blood flow and intraocular pressure (IOP) in eyes of primary chronic angle closure glaucoma patients already on concomitant timolol and pilocarpine. Thirty two patients of bilateral primary chronic angle closure glaucoma (PCACG) on topical timolol 0.5% twice a day and pilocarpine 2% three times daily were switched over to bimatoprost 0.03% once daily in both eyes. Intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) were recorded before and after starting bimatoprost and were followed up every four weeks for three months. Bimatoprost had statistically significant (p < 0.05) mean IOP reduction from 19.3 +/- 6.6 to 13.5 +/- 4.5 mmHg (30.5%) and there was improvement from 858 +/- 260 to 1261 +/- 321 microL/min (46.8%) in mean pulsatile ocular blood flow (p < 0.05). Conjunctival hyperemia (32%) was the most common adverse effect of bimatoprost. Bimatoprost 0.03% monotherapy improved ocular blood flow and provided a better diurnal IOP control than concomitant timolol-pilocarpine in eyes with primary chronic angle closure glaucoma and was found to be well tolerated.