Objectives: Author contact can enhance the quality of systematic reviews. We conducted a systematic review of the practice of author contact in recently published systematic reviews to characterize its prevalence, quality, and results. Study Design and Setting: Eligible studies were systematic reviews of efficacy published in 2005-2006 in the 25 journals with the highest impact factor publishing systematic reviews in clinical medicine and the Cochrane Library, identified by searching MEDLINE, EMBASE, and the Cochrane Library. Two researchers determined whether and why reviewers contacted authors. To assess the accuracy of the abstracted data, we surveyed reviewers by e-mail. Results: Forty-six (50%) of the 93 eligible systematic reviews published in top journals and 46 (85%) of the 54 eligible Cochrane reviews reported contacting authors of eligible studies. Requests were made most commonly for missing information: 40 (76%) clinical medicine reviews and 45 (98%) Cochrane reviews. One hundred and nine of 147 (74%) reviewers responded to the survey, and reported a higher rate of author contact than apparent from the published record. Conclusion: Although common, author contact is not a universal feature of systematic reviews published in top journals and the Cochrane Library. The conduct and reporting of author contact purpose, procedures, and results require improvement. © 2008 Elsevier Inc. All rights reserved.