AIMS To estimate the occurrence of early cataract among patients with Down's syndrome and to evaluate the clinical characteristics of the cases. METHODS Cases with Down's syndrome were ascertained from a cohort of all Danish children between 0 and 17 years of age, who were diagnosed with cataract during the period 1977-2001 (n = 1027). Information on the patients was obtained from the medical records. RESULTS Of the total of 1027 cases with non-traumatic, non-acquired cataract there were 29 cases (13 males, 16 females) with Down's syndrome (2.8%). This corresponds to an occurrence of early cataract among patients with Down's syndrome of 1.4%; 27 had bilateral cataract and two had unilateral cataract. Half of the patients (n = 14) underwent cataract surgery, of whom two had bilateral primary lens implantation. 10 patients had bilateral cataract observed soon after birth, and five of these underwent cataract surgery within the first 6 months of life. CONCLUSION The frequency of early cataract among children with Down's syndrome is estimated to be 1.4%, with cataracts requiring surgery during childhood being even rarer. In one third of the 29 cases, bilateral cataract was detected in the neonatal period.