BACKGROUND: Plant-based diets are increasingly popular and have many well-established benefits for health and environmental sustainability. Our objective was to perform a systematic review of plant-based diets and prostate cancer. METHODS: We performed a systematic database and citation search in February 2022. Studies were included if they reported primary data on plant-based dietary patterns (i.e., vegan, vegetarian, plant-based) and incidence among at-risk men for prostate cancer, or oncologic, general health/nutrition, or quality of life outcomes among patients with prostate cancer or caregivers. RESULTS: A total of 32 publications were eligible for the qualitative synthesis, representing 5 interventional and 11 observational studies. Interventional studies primarily focused on lifestyle modification including plant-based diets for men on active surveillance for localized prostate cancer or with biochemical recurrence after treatment, showing improvements in short-term oncologic outcomes alongside improvements in general health and nutrition. Observational studies primarily focused on prostate cancer risk, showing either protective or null associations for plant-based dietary patterns. Studies of the vegan diet consistently showed favorable associations with risk and/or outcomes. Gaps in the current literature include impact for long-term disease-specific outcomes. CONCLUSIONS: Interventional studies showed generally favorable results of lifestyle modifications incorporating a plant-based diet with prostate cancer outcomes as well as improvements in nutrition and general health. Observational studies demonstrated either a lower risk of prostate cancer or no significant difference. These results are encouraging in light of the many benefits of plant-based diets for overall health, as well as environmental sustainability and animal welfare.