This paper presents an analysis of a clinical case of toxoplasmosis in cats with multiple organ failure. A domestic cat at the age of six was admitted to the veterinary center of St. Petersburg. Earlier, the animal was diagnosed with feline immunodeficiency virus (FIV). It should be noted that a loss of appetite, depression, hyperthermia, labored breathing, coughing, and diarrhea became apparent after the cat had caught and eaten a bird that had flown into the dwelling a month earlier. A biochemical analysis of the animal's blood revealed hyperbilirubinemia (13.2 µmmol/L) and thrombocytopenia (74.0). An ultrasound examination revealed decreased intestinal peristalsis, enlarged mesenteric lymph nodes, hepatomegaly, and hyperemia. Radiologically, multiple small nodules were detected in the lungs. Pathologic foci were distributed bilaterally and asymmetrically, mainly in the lower parts of the lungs. A cytologic examination of the cat's bronchoalveolar mucus and peritoneal fluid revealed trophozoites of Toxoplasma gondii. DNA fragments belonging to T. gondii were identified using real-time PCR. The etiotropic and symptomatic therapies delivered to the cat under in-patient conditions were unsuccessful, and the outcome of the disease was fatal. In analyzing this clinical case, the following conclusions were made: T. gondii infestation cannot be excluded in the case of apartment-dwelling animals. The pathogen probably entered the cat's body by the cat eating a bird with T. gondii trophozoites in its organs and tissues. If a cat with a reduced immune status shows clinical signs such as enlarged lymph nodes, lethargy, decreased appetite, weight loss, nasal discharge, cough, intestinal disorders, a diagnosis of toxoplasmosis should be confirmed or excluded by serologic, PCR, or ELISA tests. Toxoplasmosis in animals with a reduced immune status can lead to severe systemic disorders, including damage to the digestive and respiratory systems, the liver, and other organs. The cumulative failure of several functional systems, developing as a terminal stage of the acute course of toxoplasmosis, can be fatal.