BACKGROUND: Serious lapses in patient care result from failure to follow-up test results. OBJECTIVE: To systematically review evidence quantifying the extent of failure to follow-up test results and the impact for ambulatory patients. DATA SOURCES: Medline, CINAHL, Embase, Inspec and the Cochrane Database were searched for Englishlanguage literature from 1995 to 2010. STUDY SELECTION: Studies which provided documented quantitative evidence of the number of tests not followed up for patients attending ambulatory settings including: outpatient clinics, academic medical or community health centres, or primary care practices. DATA EXTRACTION: Four reviewers independently screened 768 articles. RESULTS: Nineteen studies met the inclusion criteria and reported wide variation in the extent of tests not followed-up: 6.8% (79/1163) to 62% (125/202) for laboratory tests; 1.0% (4/395) to 35.7% (45/126) for radiology. The impact on patient outcomes included missed cancer diagnoses. Test management practices varied between settings with many individuals involved in the process. There were few guidelines regarding responsibility for patient notification and follow-up. Quantitative evidence of the effectiveness of electronic test management systems was limited although there was a general trend towards improved test follow-up when electronic systems were used. LIMITATIONS: Most studies used medical record reviews; hence evidence of follow-up action relied upon documentation in the medical record. All studies were conducted in the US so care should be taken in generalising findings to other countries. CONCLUSIONS: Failure to follow-up test results is an important safety concern which requires urgent attention. Solutions should be multifaceted and include: policies relating to responsibility, timing and process of notification; integrated information and communication technologies facilitating communication; and consideration of the multidisciplinary nature of the process and the role of the patient. It is essential that evaluations of interventions are undertaken and solutions integrated into the work and context of ambulatory care delivery.