During the 1970s, there was an epidemic of neonatal convulsions occurring in apparently normal babies during the fourth and fifth days of life. This syndrome was noted in France as well as in Australia. A study was undertaken to review the King George V Hospital (KGV) experience with these 'fifth day fitters'. All cases of neonatal convulsions at KGV during the years 1972-85 were reviewed. A total of 94 cases of fifth day fits occurred during this period, accounting for 57% of all neonatal convulsions occurring during 1972-79. The fits occurred in healthy term infants after an uncomplicated pregnancy. They appeared on the fourth and fifth days of life. The seizures lasted an average of 24 h, were refractory to drug therapy and, despite extensive investigation, no cause was found. The infants were assessed as normal at the time of discharge from hospital. Follow-up of these infants was incomplete. However, from the data available, it cannot be assumed to be a benign entity. The 'fifth day fit' syndrome reached epidemic proportions at a number of maternity units during the 1970s. At KGV, no case has been observed since 1982.