Purpose: The efficacy of population-based vision screening is hampered by unsuccessful referral after a positive screening test. We studied the nature and causes of unsuccessful referral in a 7-year birth cohort study of vision screening in Rotterdam, the Netherlands. Methods: All parents of children who had been unsuccessfully referred were asked whether they recalled the referral. Reasons for noncompliance, if any, were identified using semi-structured interviews. Screening records were checked for written evidence of the referral. The parents' fluency in Dutch and their socioeconomic status were also assessed. Results: Of the 561 screen-positive children, 129 (23%) had not been referred successfully. For the current study, 97 parents were successfully contacted. Of these, 14 parents had been willingly noncompliant and 83 said they were unaware of the referral, with 47% having poor to moderate fluency in Dutch. In 53 cases, the screening charts contained no written evidence of any referral. Amblyopia was identified in 3 of the unsuccessful referrals. Conclusions: In this population-based screening program, 1 of 4 positively screened children was not successfully referred. Apart from parental noncompliance, the unsuccessful referrals can be explained by miscommunication, deficient documentation, and physician noncompliance with screening guidelines. An effective monitoring feedback system may improve the efficacy of child vision screening. © 2011 by the American Association for Pediatric Ophthalmology and Strabismus.