A case of paracetamol overdose in a 36 week pregnant woman is described. The baby was delivered by Caesarian section 6 h after the overdose. The mother but not the baby was treated with N-acetylcysteine and neither suffered liver damage. The plasma paracetamol half-life was prolonged to 10 h in the neonate compared to 2.5 h in the mother and was unaffected by a two volume exchange transfusion. The pattern of urinary metabolites in the neonate was similar to that observed in the mother, but there was a marked delay in the time taken to reach peak plasma concentrations of metabolites. This is consistent with a very slow biotransformation of the drug and may explain the relative resistance of very young children to the hepatotoxicity of paracetamol. There was no evidence of limited or decreasing capacity in sulphate conjugation nor was sulphation the major metabolic pathway. In retrospect both the obstetrical intervention and the exchange transfusion were unnecessary.