We report the case of a prolonged neuromuscular blockade in an 18-month-old age girl following administration of a usual dose of succinylcholine. The diagnosis was highly suggested by the clinical history while cholinesterase activity was included in adult normal values but below values of a personal series of 41 small children. The familial analysis of dibucaine and fluoride number confirmed the hypothesis of an atypical variant (AA phenotype). The cholinesterase activity is higher in small children than in adult and has to be analysed according to the age.