A population-based case-control study of 416 histologically diagnosed, incident gliomas in adults was carried out in Melbourne, Australia, to determine whether past medical, family or reproductive histories are risk factors for developing glioma. A total of 422 controls were selected from the Australian electoral roll and matched to cases for age, sex and post code of residence. An increased risk of developing glioma was observed among first-born individuals OR (95% CI) 2.0 (1.4-2.9). It is possible that this effect is due to residual confounding by socio-economic status or that it is a chance finding. Alternatively, it may be that this is due to some other effect linked to the first pregnancy, such as maternal age, birth weight or circumstances of delivery. There was no apparent association between the development of glioma and other neuropsychiatric or general medical conditions or with family history or reproductive history. Allergies (asthma and eczema) were not associated with a decreased risk of glioma, as has previously been suggested. Glioma is the most common primary brain malignancy in adults, accounting for approximately 75% of all primary adult brain tumours (Green et al., 1976). The prognosis is poor, with a median survival of less than 12 months (Axtell et al., 1983;Whittle et al., 1991) and an increasing incidence over the last 30 years (Davis et al., 1991). The causes of glioma are unknown, and related to this, no preventive strategy is available. Although many possible risk factors for brain tumours have been suggested, there is still no dominant hypothesis. A wide range of genetic and environmental factors have been investigated. While some evidence exists implicating certain work chemicals (Burch et al., 1987;Preston-Martin and Mack, 1991;Morrison et al., 1992), investigations of a wide range of genetic and environmental factors have been inconclusive (Burch et al., 1987;Wrensch and Barger, 1990;Schiffer, 1991;Ryan et al., 1992;Zampieri et al., 1994).A role has been suggested for genetic factors in the aetiology of glioma (Schiffer, 1991;Wrensch and Barger, 1990), but this is not consistent in all studies (Choi et al., 1970). This is based on the following: the difference in distribution of ABO blood groups between brain tumour patients and controls (Selverstone and Cooper, 1961;Zampieri et al., 1994), the association of brain tumours with genetically determined disorders (Schiffer, 1991), some evidence of familial aggregation of brain tumours (Schiffer, 1991) and familial clustering of brain tumours with breast and lung cancers (Wrensch and Barger, 1990;Zampieri et al., 1994).A number of exploratory case-control studies have been reported which examine the association of medical conditions, family and reproductive history in cases with glioma and controls. There are few consistent findings. There is some evidence that allergies may decrease the risk of glioma (Hochberg et al., 1990;Ryan et al., 1992;Schlehofer et al., 1992a). Although in one report the authors suggested that the reproductive a...