Abstract Objectives Flavonoids are a diverse group of plant constituents with demonstrated neuroprotective and anti-tumor effects. Flavonoid intake may decrease glioma risk, an association that has not yet been investigated in humans. The objective of this study was to evaluate the association between dietary flavonoid consumption and glioma risk in participants in the female Nurses’ Health Study (1984–2014, n = 81,688) and Nurses’ Health Study II (1991–2017, n = 95,228), and the male Health Professionals Follow-up Study (1986–2014, n = 49,884). Methods Exposure was average long-term (up to 30 years) and recent (up to 12 years) intake of total flavonoids and six flavonoid subclasses, derived from validated quadrennial food frequency questionnaires. The primary outcome was incident glioma, confirmed by medical record review. Results We documented 536 incident cases of glioma across 5,936,386 person-years of follow-up. Long-term total flavonoid, flavan-3-ol, and polymer intake was associated with decreased glioma risk in pooled analyses comparing highest to lowest quintile of consumption (total flavonoid hazard ratio (HR) = 0.79, 95% CI: 0.59–1.05, P-trend = 0.04; flavan-3-ol HR = 0.76, 95% CI: 0.57–1.01, P-trend = 0.04; polymer HR = 0.82, 95% CI: 0.61–1.09, P-trend = 0.05). Associations with recent intake were weaker and not statistically significant. There were no associations with other flavonoid subclasses. After additional adjustment for tea consumption, there was no significant association between flavan-3-ol or polymer consumption and glioma. Conclusions Increased dietary intake of flavan-3-ol and polymeric flavonoids, especially those predominant in tea, was associated with decreased glioma risk in a prospective cohort of men and women. Habitual consumption of foods and beverages containing flavan-3-ols and polymeric flavonoids may protect against the development of glioma. Funding Sources This work was supported by the U.S. National Institutes of Health.