This report describes an infant who was born to a mother with chronic pain treated with fentanyl 100 microg/h transdermal patch throughout her pregnancy and during lactation. On day of life 27, when the baby was feeding and gaining weight on maternal milk, samples of the baby's blood and maternal milk were sent for analysis. The mother's milk fentanyl level was 6.4 ng/ mL. The infant's blood fentanyl level was undetectable. This preliminary report suggests that fentanyl transdermal patch treatment might be a viable option for managing chronic pain during lactation.