The Rapid Assessment of Avoidable Blindness (RAAB) has been developed as a simple and rapidsurvey methodology that can provide data on the prevalence and main causes of blindness.AimTo assess the prevalence and main causes of avoidable blindness and visual impairment in peopleaged 50 and above in Mongolia.MethodsThe RAAB uses a standard methodology which is documented in the RAAB Instruction Manual (HansLimburg, International Centre for Eye Health, London School of Hygiene and Tropical Medicine).Assuming an estimated prevalence of blindness in persons aged 50+ of 2.14% and a non-complianceof 5%, with a variation to 25% around the estimate of 2.14% at 95% probability, the required samplesize was calculated at 4,040: 101 clusters of size 40. Visual acuity (VA) was measured with a Snellentumbling E chart, using optotype size 18 (60) on one side and size 60 (200) on the other side. Thelens status of all participants was assessed by both torch and distant direct ophthalmoscopy, by anophthalmologist in a shaded or dark environment. The data were analyzed using RAAB Version 4.02(ICEH, London) for pre-defined reports relating to both crude and age and gender adjusted results.ResultsThe survey included 4,040 people aged 50 years and older, of whom 4,029 were actually examined.The coverage was 99.7%. 7 persons (0.2%) were absent and 4 (0.1%) refused to participate in thestudy. The prevalence of bilateral blindness with available correction in the better eye is 2.2 % (95% CI,1.7 - 2.7%); 2.4% in males and 2.2% in females. The prevalence of bilateral severe visual impairment(SVI) is 2.1% and bilateral moderate visual impairment (MVI) is 10.8%. The prevalence of functionallow vision, requiring low vision services, is 4.5%. In people aged 50+, untreated cataract is the mostcommon cause of bilateral blindness with 38.9%, followed by glaucoma (20.0%), non-trachomatouscorneal opacity (13.3%), and other posterior segment disease (7.8%).Conclusion: Untreated cataract and uncorrected refractive errors are the major causes of avoidableblindness and low vision in Mongolia, respectively. Priority should be given to cataract surgery,followed by the development of optical services and PHC and PEC services, as these are the mostcost-effective interventions. These three interventions will address about three thirds (67.8%) of thecauses of blindness and have most impact.