Human activities dramatically increased the amount of reactive nitrogen in the environment through the widespread production and application of fertilizers, generation of human and livestock waste, and combustion of fossil fuels. This excessive nitrogen load eventually reaches water bodies and at circumneutral or acidic pH accumulates in the form of nitrate, nitrite, and ammonium. Our objective was to test if prolonged exposure to low and environmentally relevant concentrations of nitrate, nitrite, and ammonium could affect survivorship, growth, and behavior of tadpoles of a Brazilian amphibian species, the gladiator frog Hypsiboas faber. Tadpoles of H. faber were exposed to 0, 2.5, and 10 mg.L⁻¹ of nitrogen as nitrate, nitrite, and ammonium in a 21-day static renewal test. We demonstrated that under prolonged exposure even relatively low concentrations of inorganic nitrogen can cause lethal and sublethal effects on anuran larvae. Nitrate, the most abundant form of nitrogen in nature, caused no effects even in the largest manipulated concentration. Tadpoles exposed to 10 mg.L⁻¹ N-nitrite had decreased growth and survivorship relative to controls. However, such nitrite concentrations are uncommon and generally found only in highly polluted, anaerobic conditions. In turn, tadpoles exposed to 10 mg.L⁻¹ N-ammonium (which is within the upper range of concentrations observed in nature) had reduced activity rates and survivorship relative to controls. Future studies that aim to assess the environmental risk of nitrogen contamination should expand monitoring of concentrations in natural habitats, assess ontogenetic variation in organismal sensitivity, and evaluate the effects of synergistic interactions between inorganic nitrogen and other physical, chemical, or biological stressors to amphibian larvae.