BACKGROUND: There are no reports on hyponatremia and acute kidney injury (AKI) involved in the course of HIV-related toxoplasmic encephalitis (TE). The main objective of this study was to describe the occurrence of hyponatremia and its relationship with AKI and mortality in HIV-related toxoplasmic encephalitis (TE). METHODS: This was a retrospective cohort study on patients with HIV-related TE. AKI was considered only when the RIFLE (risk, injury, failure, loss, end-stage) criterion was met, after the patient was admitted. RESULTS: A total of 92 patients were included, with a mean age of 36 ± 9 years. Hyponatremia at admission was observed in 43 patients (46.7%), with AKI developing in 25 (27.1%) patients during their hospitalization. Sulfadiazine was the treatment of choice in 81% of the cases. Death occurred in 13 cases (14.1%). Low serum sodium level correlated directly with AKI and mortality. Male gender (OR 7.89, 95% CI 1.22-50.90, p = 0.03) and hyponatremia at admission (OR 4.73, 95% CI 1.22-18.30, p = 0.02) were predictors for AKI. Independent risk factors for death were AKI (OR 8.3, 95% CI 1.4-48.2, p < 0.0001) and hyponatremia (or 9.9, 95% ci 1.2-96.3, p < 0.0001). CONCLUSION: AKI and hyponatremia are frequent in TE. Hyponatremia on admission is highly associated with AKI and mortality.