Abstract Background Nitrates and nitrites occur naturally in water and soil. They are also used as food additives (preservatives) in processed meats. They could play a role in the carcinogenicity of processed meat. The objective was to investigate the relationship between nitrate and nitrite intakes (natural food, water and food additive sources) and cancer risk in a large prospective cohort with detailed dietary assessment. Methods Overall, 101 056 adults from the French NutriNet-Santé cohort (2009–ongoing, median follow-up 6.7 years) were included. Nitrites/nitrates exposure was evaluated using repeated 24-h dietary records, linked to a comprehensive composition database and accounting for commercial names/brands of industrial products. Associations with cancer risk were assessed using multi-adjusted Cox hazard models. Results In total, 3311 incident cancer cases were diagnosed. Compared with non-consumers, high consumers of food additive nitrates had higher breast cancer risk [hazard ratio (HR) = 1.24 (95% CI 1.03–1.48), P = 0.02], more specifically for potassium nitrate. High consumers of food additive nitrites had higher prostate cancer risk [HR = 1.58 (1.14–2.18), P = 0.008], specifically for sodium nitrite. Although similar HRs were observed for colorectal cancer for additive nitrites [HR = 1.22 (0.85–1.75)] and nitrates [HR = 1.26 (0.90–1.76)], no association was detected, maybe due to limited statistical power for this cancer location. No association was observed for natural sources. Conclusion Food additive nitrates and nitrites were positively associated with breast and prostate cancer risks, respectively. Although these results need confirmation in other large-scale prospective studies, they provide new insights in a context of lively debate around the ban of these additives from the food industry.