To determine the risk of non-arteritic anterior ischaemic optic neuropathy (NAION) after cataract extraction (CE) in the fellow eye of patients with prior unilateral NAION.Retrospective, cohort study.Medical records of patients with NAION evaluated in our institution between 1 January 1986 and 31 December 2001 were reviewed to determine the onset of NAION and the time of CE. Patients were excluded if the date of NAION and CE was unreliable, or if CE in the fellow eye was performed before the unilateral NAION. Statistical analysis was performed by including fellow eye CE as a time-dependent covariate in a Cox proportional hazards regression model of NAION incidence in the fellow eye.Of the 325 eligible patients, 9 (53%) of 17 patients with NAION who underwent CE in the fellow eye developed fellow eye NAION, and 59 (19%) of 308 patients with NAION who did not undergo CE in the fellow eye developed fellow eye NAION. Cataract extraction in the fellow eye increased the risk of NAION occurrence in the fellow eye by 3.6-fold (Cox regression, p=0.001).Patients with unilateral NAION are at a significantly higher risk of developing NAION in the fellow eye after CE.