AbstractBACKGROUNDThere are few published studies on microtia‐anotia frequency.METHODSUsing data from birth defects surveillance programs around the world, we conducted a systematic review on the frequency of microtia‐anotia to further explore the differences in prevalence across countries. Ninety‐two birth defects surveillance programs were evaluated with a total of 8917 cases of microtia‐anotia. We computed the prevalence per 10,000 births for each surveillance program for total cases of microtia‐anotia (microtia types I to IV), microtia (types I to III), and anotia (type IV). Prevalence ratios were calculated by large geographic areas, race/ethnicity, and by surveillance methodologies.RESULTSThe overall prevalences were: microtia‐anotia, 2.06 (confidence interval [CI], 2.02–2.10); microtia, 1.55 (CI, 1.50–1.60); and anotia 0.36 (CI, 0.34–0.38). Higher prevalences were observed for the Americas, Northern Europe and Asia, among Hispanics and Asians, and among active ascertainment and hospital‐based surveillance programs.CONCLUSIONSWe observed marked variation in the prevalence of microtia‐anotia across surveillance programs and within countries. These results must be interpreted cautiously as this variability may be explained mainly by differences in surveillance methods. However, given the magnitude of some of the differences, other factors may also be involved. This study contributes to the knowledge of the prevalence of microtia‐anotia by providing a critical analysis of the existing data. In addition, it supports the need for a coding system that allows complete phenotype characterization of microtia‐anotia, including severity and laterality, as well as for further studies on the variation of its frequency related to race and ethnicity. Birth Defects Research (Part A), 2011. © 2011 Wiley‐Liss, Inc.