Purpose: To investigate the epidemiology of aniridia in the populations of Sweden and Norway. Methods: A thorough search for aniridia patients has been performed in Sweden and Norway. All participants had a clinical ophthalmological examination documented through photography. Blood samples were taken for mutation analysis and pedigrees were established. Results: A total of 181 patients with aniridia were identified in the two countries. This gives an age-specific prevalence of 1:72 000 in the entire region, 1:70 000 in Sweden and 1:76 000 in Norway. A total of 124 individuals (69%) were examined. Male/female ratio was 0.94 (Sweden 0.85 and Norway 1.2). Mean age of the examined patients was 29 years and median age 25 years. We did not find any significant age difference between the two countries. The mean visual acuity (VA) was 0.19 (Sweden 0.19 and Norway 0.18).The number of families with more than one affected member was 31 and the number of sporadic cases was 40. Conclusion: We have done a thorough search of the literature, but we have found no earlier studies describing aniridia in an entire country and only a few reports from larger areas. We assume that most aniridia patients have been found and the aniridia prevalence of 1:72 000 can be regarded as well supported. Further studies on other aspects of aniridia are in progress, and information from these can contribute to guidelines for the care of patients with this rare but serious disease.