<p>The accurate identification of gametes, embryos, and patients is a fundamental requirement for the intended treatment in the context of assisted reproductive technology (ART). Embryo mix-ups are among the most serious errors in ART and are considered highly sensitive, which can impede error management and the identification of error sources. Here, we present five cases of embryo mix-ups that occurred at five different ART facilities. These reports highlight misidentification of patients and specimens as underlying factors in all five mix-up cases and emphasize the importance of facility-wide root cause analysis to improve process safety for patients and staff. Although human error was an important factor, the underlying conditions that make these critical errors possible must be identified to allow for effective risk mitigation. In all cases, a sequence of errors led to embryo mix-ups that could have been prevented by adherence to clear institutional guidelines and workflows regarding patient identification and verification of patient and sample identities prior to embryo transfer. It is important that operating guidelines are integrated into daily work routines and ART facilities have control systems in place to monitor critical steps and allow for the detection of error sources or faulty processes to prevent subsequent damage.</p>