BACKGROUND: Oligodendroglial tumors are unique subtypes of brain tumors often combined with other miscellaneous glial tumors during data analysis because of the small numbers in any one study. However, individuals with oligodendroglial tumors have different demographic, clinical, and survival characteristics than individuals with other glial histologies, making it important to evaluate risk factors separately. MATERIALS AND METHODS: We collected data on oligodendroglial tumor cases (oligodendrogliomas, anaplastic oligodendrogliomas, and oligoastrocytomas) from five case-control studies of adult gliomas. Two controls per case were frequency-matched on race, gender, age 65 years, and study site. We reviewed the questionnaires from each study, and we determined the variables that were common between studies or variables that could be used to create new common variables. We calculated the univariate statistics, and we estimated the odds ratios (ORadj) and 95% confidence intervals (CI) adjusted for age group, gender, race, study site, and year of interview using logistic regression analysis. RESULTS: Overall, 556 cases, including 298 oligodendrogliomas, 130 anaplastic oligodendrogliomas, and 128 oligoastrocytomas (mixed gliomas), and 1,128 controls were compiled. Fifty-three percent of the study participants were male, 90% were Caucasian, and the average age at diagnosis/interview was 44 years. The gender and race frequencies and mean age at diagnosis/interview were similar between cases and controls. In a preliminary data analysis, anaplastic oligodendroglioma cases were more likely than controls to have reported a family history of brain tumors (ORadj 5 3.1 [95% CI, 1.4-6.9]). Cases with anaplastic oligodendrogliomas or oligoastrocytomas were less likely than controls to report a history of asthma or allergies combined (ORadj 5 0.4 [95% CI, 0.2-0.6] and 0.3 [95% CI, 0.2-0.7], respectively). An inverse relationship was also found between a history of chicken pox and oligodendroglioma (ORadj 5 0.7 [95% CI, 0.4-1.0]) or anaplastic oligodendroglioma (ORadj 5 0.5 [95% CI, 0.3-0.9]). Oligodendroglioma cases were less likely than controls to have used bottled water or "other" water source compared to a public water source (ORadj 5 0.4 [95% CI, 0.2-1.0] and 0.3 [95% CI, 0.1-0.7], respectively). Epilepsy and/or seizures were associated with an increased risk in all three histology groups, but these may be symptoms of a preclinical disease rather than a risk factor. Results were similar when the data were restricted to cases that underwent a pathology review. CONCLUSIONS: Pooling data from several sources has provided an opportunity to investigate etiologic factors in a rare brain tumor subtype. While several factors associated with oligodendroglial tumors are similar to those identified for the broad glioma grouping, some differences in the relationships by histology subtype were apparent. Additional analyses will be presented.