Elevated maternal body temperature during pregnancy is of clinical concern as side effects have been reported. We estimated the association between maternal fever and sauna bathing during pregnancy and risk of epilepsy in the offspring. We identified 86,810 liveborn singletons from the Danish National Birth Cohort (DNBC) and followed them for up to 9 years of age. Information on fever including number, timing, level, duration, and symptoms of each fever episodes was collected in two computer-assisted telephone interviews around 17 and 32 gestational weeks; information on maternal use of a sauna was collected in the latter interview, and information on epilepsy was obtained from the Danish National Hospital Register. We applied Cox regression models to estimate the incidence rate ratios (IRR) of epilepsy for children exposed to maternal fever and sauna bathing during pregnancy. Maternal sauna bathing during pregnancy was not associated with an increased risk of epilepsy. Maternal fever during pregnancy in general was not associated with an increased risk of epilepsy in the offspring [IRR = 1.01, 95% confidence interval (CI) 0.85, 1.19], and no dose-response pattern was found according to number, level and duration of fever. However we did find an increased risk of epilepsy among children exposed to at least 3 fever episodes (IRR = 1.88, 95% CI 1.19, 2.98), to maternal fever with symptoms in the urinary system (IRR = 4.86, 95% CI 1.56, 15.17), and to one-day maternal fever of 39.0-39.4?C (IRR = 2.79, 95% CI 1.60, 4.84). Our findings do not support a strong association between hyperthermia and epilepsy but the associations between underlying causes of fever, especially prenatal infections, call for more research.