The unusually high population frequency of a germline TP53 mutation (R337H) predisposing to early cancer has led to mass newborn testing for this mutation in the State of Paraná, southern Brazil. Newborn screening for inherited cancer risk is complex and controversial. In this paper, we discuss the justifications for this screening by considering the medical and scientific evidence for this mutation. R337H has been identified in Brazilian families with Li-Fraumeni or related syndromes predisposing to cancers in childhood (ie, brain, renal, and adrenocortical carcinomas), adolescence (ie, soft tissue and bone sarcomas), and young adulthood (ie, breast cancer). R337H has also been detected in children with adrenocortical carcinoma without a documented family history of cancer. The mutation is estimated to occur in about 0·3% of the population in southern Brazil and is associated with increased cancer risk throughout life. Cancer patterns in families positive for R337H suggest strong genetic modifying effects, making it difficult to predict individual risk. Because protocols for cancer-risk management in Li-Fraumeni or related syndromes are debatable, extreme care should prevail in predictive testing of children for R337H. A detailed assessment of the risks, benefits, and costs is needed to ensure that medical, social, and ethical justifications for newborn screening are met.