Aim Analysis of age at time of detection and surgery of dense unilateral cataract and investigation of best‐corrected visual acuity (BCVA) in a nationwide register‐based cohort study, based on the routine of maternity ward eye screening. Methods Data were derived from the Paediatric Cataract Register (PECARE). All children (n = 54) diagnosed with dense congenital unilateral cataract between January 2007 and September 2014 who had surgery before 1 year of age, and for whom 5‐year follow‐up records were available, were included. Results The majority, 35/54 (65%), were detected and operated on before age 6 weeks and 30/35 (86%) were referred from maternity wards. Visual acuity (VA) ≥ 0.5 (decimal, 0.3 logMAR) was found in 7/53 (13%) of the cohort at age 5 years; further, 19 children achieved VA ≥ 0.1 (decimal, 1.0 logMAR) (36%) and 19 children VA < 0.05 (decimal, 1.30 logMAR) (36%). Ten‐year follow‐up records were available for 17/53 (32%) children; 1/17 (6%) achieved VA ≥ 0.5 (decimal, 0.3 logMAR), 4/17 (24%) VA ≥ 0.3–<0.5 (decimal, 0.52–0.30 logMAR), 3/17 (18%) VA ≥ 0.05–0.1 (decimal, 1.30–1.0 logMAR) and 10/17 (59%) VA < 0.05 (decimal, 1.30 logMAR). Conclusion A total of 90% of the children were detected with cataract within 100 days of birth and 80% were operated on within this period. This study showed better visual acuity in those treated for dense unilateral cataracts than previously reported in an earlier Swedish cohort study.