The recurrence rate of gestational diabetes in 58 patients who had had the foregoing pregnancy complicated by diabetes was estimated to be 30% if our former criteria for abnormal glucose tolerance were strictly applied and 25% if our new, more stringent criteria were used. The recurrence rate is not influenced by prophylactic administration of pyridoxine. The perinatal morbidity complicating the 'second' pregnancy of former gestational diabetics was not increased in those patients who were not treated again, as compared with those who were. Recurrent gestational diabetes is associated with a degree of overdiagnosis in an attempt to detect all gestational diabetics. It is suggested that recurrent gestational diabetes occurs mainly in prediabetic patients.