The aim of our study was to investigate whether reproductive factors influence the risk of primary brain tumours (PBT) in offspring.Data on all deliveries in two Swedish counties from 1955 to 1990 were extracted from two birth registries. The follow-up period closed at the end of 1994, with subjects followed up to early middle age. Incidence rates of malignancy for 1958-1994 were obtained from the Swedish Cancer Registry. Standardised incidence ratios (SIR) and relative risks were calculated for astrocytomas, primitive neuroectodermal tumour, ependymoma and meningiomas in offspring.Few associations were detected. High birth weight indicated an increased risk for astrocytomas grade I and II for all primary brain tumours, and the risk was close to significance for astrocytomas grade I-II (SIR = 3.64; CI = 0.98-9.31). For children under 15 years of age the risk for astrocytomas grade I and II was further increased (SIR = 4.44; CI = 1.19-11.38).A consistent pattern of non-association indicated a low impact of intrauterine environment on the future development of primary brain tumours in offspring up to early middle age.