Missed or delayed cancer diagnoses are a frequent cause of malpractice lawsuits in the ambulatory setting. This systematic review sought to characterize the existing literature on diagnostic error for four common types of cancer. Although few prospective studies were found, the authors concluded that missed and delayed diagnoses were common and harmful. Five domains were identified that contribute to preventable delays in diagnosis, ranging from system factors (such as delays in obtaining appointments) to physician and patient factors. Prior studies that were included in this review examined the frequency of incorrect pathologic diagnoses and factors predisposing to pathology errors.