Aims.To estimate the incidence of ac ute-onset presumed infectious endophthalmitis(PIE)following cataract surgery in the UK and provide epidemiologica l data on the pre-sentation,management,microbiolo gy,and outcome of cases of endophthalmitis.Methods.Cases were identified prospectively by active surveillan ce through the British Ophthalmological Surveillance Uni t reporting card system,for the 12-month period October 1999to September 2000inclusive.Questionnaire data were obtained from ophthal-mologists throughout the UK at baseline and 6months after diagnosis.Under-reporting was estimated by independently contacting units with infection databases.Results.Data were available on 213patients at baseline and 201patients at follow-up.The minimum estimated incidence of PIE was0.086per 100cataract extractions a nd the corrected inci-dence was 0.14per 100cataract extra ctions.For the management of PIE,96%of patients re ceived intravitreal,30%subconjunctival,65%oral,and 17%intravenous antibiotics.In all,17%of patients received intravitreal steroid.From the intraocular sampl es taken for microbio-logical analysis,56%were culture p ositive.At follow-up,48%of patients achieved visual acui ty of 6/12or better and 66%achieved better than 6/60.13%of patients were unable to perceive light or had evisc eration of the globe.Conclusions.The incidence of PIE after cataract surgery in the UK is comparable to that of other s tudies.Approxi-mately 50%of patients achieved a vis ual acuity close to the driving standard. Aims.To estimate the incidence of ac ute-onset presumed infectious endophthalmitis (PIE) following cataract surgery in the UK and provide epidemiologica l data on the pre-sentation, management, microbiolo gy, and outcome of cases of endophthalmitis. Methods. Cases were identified prospectively by active surveillan ce the the British Ophthalmological Surveillance Uni reporting media system for the 12-month period October 1999 to September 2000 inclusive. Quality of data were obtained from ophthal-mologists throughout the UK at baseline and 6 months later diagnosis. Unit-reporting was estimated by independently contacting units with infection databases.Results. Data were available on 213patients at baseline and 201patients at follow-up. minimum minimum incidence of PIE was0.086per 100cataract extractions a nd the corrected inci-dence was 0.14per 100cataract extra ctions. For the management of PIE, 96% of patients re ceived intravitreal, 30% subconjunctival, 65% oral, and 17% intravenous antibiot ics.In all, 17% of patients received intravitreal steroid. From the intraocular sampls taken for microbio-logical analysis, 56% were culture p ositive. At follow-up, 48% of patients achieved visual acui ty of 6 / 12or better and 66% achieved better than 6 / 60.13% of patients were unable to perceive light or had evisc eration of the globe. Conclusions. The incidence of PIE after cataract surgery in the UK is comparable to that of other s tudies. Approxi-mately 50 % of patients achieved a vis ual acuity close to the driving standard.