Disclaimer: As part of our efforts to improve our practices and in accordance with the CADA’s guidance issued on February 11, 2021, the report has been withdrawn to ensure that it contains no data that could pose a risk of indirect identification. This report, which has been reviewed and brought into compliance with the CADA’s recommendations, will soon be available again on our website. Summary: Introduction In 2013, Santé publique France (Loire-Atlantique Regional Unit) was notified following a report by a hospital healthcare professional regarding a cluster of three cases of children with transverse agenesis of the upper limbs (TAUL), all residing in the same municipality located in Loire-Atlantique. In response to this report, an investigation was immediately conducted by the Santé publique France unit in Loire-Atlantique to address the report. Methods: The objectives of this investigation were 1) to validate the report based on a set of criteria (case definition, spatial criteria, temporal criteria), 2) to statistically assess whether this cluster of cases in the same municipality in Loire-Atlantique could be due to chance, and 3) to investigate for a common exposure during the pregnancies of the mothers of these three cases. To ensure that the cases had the same type of malformation—defined here as a congenital malformation unrelated to a chromosomal abnormality—they were referred for consultation with a specialist. To statistically determine whether this cluster of cases could be due to chance, two methodological approaches were used. The first approach consisted of comparing the observed number of cases of children with ATMS in the municipality where the mothers of the three children resided during their pregnancies over the period in question, with the expected number of cases over that same period, based on the average annual prevalence of ATMS, estimated from data from the six French registries for the period 2009–2014. For the second approach, the probability of observing a similar cluster of cases of children with this type of malformation in municipalities in France with the same characteristics in terms of population size and annual births was estimated. The search for a common exposure during the pregnancies of the mothers of these cases was conducted using a telephone questionnaire, developed based on the malformation reporting form used by the Rhône-Alpes registry, REMERA, and using information collected from the physician who examined the children. The BASIAS, BASOL, and ARIA databases, as well as the prefecture’s websites regarding environmental hazards and risks, were consulted to investigate environmental exposure. Results: After examination by a specialist physician, the 3 cases were considered to have ATMS. Since these children were born in two consecutive years, between 2007 and 2011, and their mothers resided in the same municipality during their pregnancies, they were considered to belong to the same cluster. The ratio of observed cases to expected cases was estimated at 87.8, with a 95% confidence interval ranging from 17 to 256, and a statistically significant p-value. In France, 10,000 municipalities had characteristics similar to the municipality where the mothers of the three children resided during their pregnancies. The probability of observing a cluster of 3 cases of children with ATMS during the 2007–2011 period in these municipalities was estimated at 6 × 10^(−6). The information gathered during this investigation of common exposure and the review of environmental databases did not identify a common exposure to a risk factor for these 3 mothers. Conclusion: The occurrence of three cases of children with ATMS, born over two consecutive years in the same municipality in Loire-Atlantique, represented an unusual health event. However, no hypothesis of common exposure was identified.