The clinical and pathological findings of a case of fatal disseminated toxoplasmosis in a captive brown-throated sloth (Bradypus variegatus) from the northern region of Brazil are reported. Clinical signs were nonspecific and included apathy, prostration, dyspnoea, and loss of appetite. Treatment with penicillin was attempted, but the animal died within five days of the onset of clinical signs. Microscopically, there was acute inflammation in the liver, spleen, and lungs associated with necrosis and a few cysts and extracytoplasmic tachyzoites, with a morphology compatible with Toxoplasma gondii. Tissue sections were submitted for immunohistochemistry that confirmed T. gondii as the aetiological agent. To the authors’ knowledge, this is the first report of toxoplasmosis in B. variegatus.