To evaluate the prevalence of ocular hypertension (OHT) and glaucoma in patients with central retinal vein occlusion (CRVO) and hemi-CRVO (HCRVO) and of the fall in intraocular pressure (IOP) secondary to CRVO/HCRVO. Nonrandomized comparative case series. We investigated 674 consecutive patients who were initially seen with unilateral CRVO (n = 548) and HCRVO (n = 126) at their onset, with a normal fellow eye. The fellow uninvolved eye in each patient acted as a control. Central retinal vein occlusion and HCRVO were categorized into nonischemic and ischemic. At all visits, patients had a detailed ocular history, as well as a thorough bilateral ocular evaluation, including IOP recording with a Goldmann applanation tonometer; when the diagnosis of OHT or glaucoma was initially uncertain, the 24-hour diurnal IOP was recorded. The observed prevalence rates of OHT and glaucoma among patients with CRVO and HCRVO were compared with those in the general population. The prevalence of OHT and glaucoma, and of ocular hypotension secondary to CRVO/HCRVO. The overall prevalence of glaucoma was 9.9% and of OHT 16.2%. The prevalence of glaucoma/OHT was found to be significantly (P<0.0001) higher in patients with CRVO and HCRVO than in the general population. There was no significant difference in the proportion of patients with glaucoma/OHT among the various types of CRVO/HCRVO (P = 0.156). Forty-eight percent of all patients had lower IOP (>/==" BORDER="0">2 mmHg) in the CRVO/HCRVO eye than in the fellow (uninvolved) eye at their initial evaluation. The prevalence of ocular hypotension was significantly (P<0.0001) higher in patients with glaucoma/OHT not on ocular hypotensive therapy than in patients without glaucoma. Among the patients without glaucoma, the prevalence of ocular hypotension differed significantly among the various types of CRVO/HCRVO (P = 0.007). Central retinal vein occlusion and HCRVO have a significant association with glaucoma and OHT and with a subsequent fall in IOP in the involved eye. Few patients with CRVO/HCRVO have high IOP in the involved eye, although many of them do have it in the fellow uninvolved eye. It is important to exclude glaucoma/OHT in the fellow eye of any patient with CRVO/HCRVO; if present, elevated IOP should be treated to reduce the risk of that eye developing (1) CRVO/HCRVO and (2) glaucomatous damage. There may be no benefit to prescribing IOP-lowering drops for involved eyes whose IOP is already normal.