PURPOSE: Metabolomic and preclinical studies suggest that branched-chain amino acids (BCAA) may be inversely associated with neurodegenerative diseases including glaucoma. We therefore assessed the long-term association between dietary intake of BCAA and incident primary open-angle glaucoma (POAG) and POAG subtypes. METHODS: We followed biennially participants of the Nurses' Health Study (NHS; 65 531 women: 1984-2016), Health Professionals Follow-up Study (42 254 men: 1986-2016) and NHSII (66 904 women; 1991-2017). Eligible participants were 40+ years old and reported eye examinations. Repeated validated food frequency questionnaires were used to assess dietary intake of BCAA. Incident cases of POAG and POAG subtypes defined by visual field (VF) loss and untreated intraocular pressure (IOP) were confirmed by medical record review. Multivariable-adjusted relative risks (MVRRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards models. RESULTS: We identified 1946 incident POAG cases. The pooled MVRRs of POAG for the highest quintile (Q5 = 17.1 g/day) versus lowest quintile (Q1 = 11.2 g/day) of total BCAA intake was 0.93 (95% CI, 0.73-1.19; ptrend = 0.45; pheterogeneity by sex = 0.24). For subtypes of POAG defined by IOP level or POAG with only peripheral VF loss, no associations were observed for men or women (ptrend ≥ 0.20); however, for the POAG subtype with early paracentral VF loss, there was a suggestion of an inverse association in women (MVRRQ5versusQ1 = 0.80 [95% CI, 0.57-1.12; ptrend = 0.12]) but not in men (MVRRQ5versusQ1 = 1.38 [95% CI, 0.81-2.34; ptrend = 0.28; pheterogeneity by sex = 0.06]). CONCLUSION: Higher dietary intake of BCAA was not associated with POAG risk.