AIMS: To assess the outcome of children referred to the hospital eye service (HES) from an orthoptist based preschool vision screening programme. METHODS: A retrospective study was conducted of children referred from screening during a 2 year period. Children were screened by community orthoptists at 3 1/2 years of age. The main outcome measures were (1) HES findings for children referred from screening, and (2) visual outcome for amblyopic children after completion of treatment. RESULTS: The attendance rate at screening was 79.3% (6794 children): 348 children (5.1% of those screened) were referred to the HES. The HES findings were refractive error (32.9%), amblyopia (29.9%), false positive referral (20.1%), strabismus (13.2%), and other ocular disorders (3.9%). The positive predictive value of screening was 79.9%. Screening detected 48 children with straight eyed amblyopia and 43 children with strabismic amblyopia. A visual acuity of 6/9 or better in the amblyopic eye was achieved by 87.2% of straight eyed amblyopes and 64.3% of strabismic amblyopes (chi 2 = 5.27, p = 0.02). Residual amblyopia of 6/24 or worse occurred in only 5.6% of amblyopic children. CONCLUSION: Most amblyopic children detected by preschool vision screening achieve a good visual outcome with treatment. While treatment earlier in the sensitive period might be expected to give improved results, it remains to be demonstrated that preschool screening results in a better outcome than screening at school entry. Preschool vision screening also detects a significant number of children without amblyopia who have reduced vision due to refractive errors. This group of children must be included in any analysis of the cost effectiveness of preschool vision screening.