Introduction. Infective Endocarditis (IE) is a serious pathology with severe complications and high mortality (20-25%). A considerable number of patients develop IE on the background of comorbidities: diabetes mellitus (DM), viral hepatitis, cirrhosis, cancer. The predominant pathogens in patients with IE are staphylococci, streptococci and enterococci. The prevalence of DM is increasing worldwide, and the proportion of DM among those with IE is high, caused by bacteremia, immunodeficiency and endothelial dysfunction. Case presentation. Patient C., 64 years old, with diagnosis: Nosocomial Infective Endocarditis of the prosthetic valve, Staphylococcus Aureus etiology, with damage to the prosthesis of the aortic valve. Regurgitation of the aortic valve 3rd degree. Valvular abscess. Sinus tachycardia. HF III NYHA. Diabetes mellitus type 2. Dyslipidemia. Toxic anemia. The patient presents fever 38ºC, chills, sweats, inspiratory dyspnea, palpitations, fatigability, weight loss. Objective data: pronounced edema in the calves, rhythmic heart sounds, FCC 120 b/min, BP 110/40mmHg, the sound of the prosthesis, diastolic murmur in the auscultation of the aortic valve. Anemia (Hb 70g/l), leukocytosis, lymphopenia, thrombocytosis, increased ESR. Blood biochemistry: hyperglycemia. Hemoculture: Staphylococcus aureus. ECG: Sinus tachycardia with FCC 120b/min. EAH left deviation. LV hypertrophy. EcoCG: medium vegetation (15 mm) on mechanical aortic prosthesis. Regurgitation of the AoV 3-rd degree. Treatment:triple antibiotic therapy, antimycotics, diuretics, without positive dynamics. Required emergency valvular surgery due to suspicion of valvular abscess, with postoperative positive dynamics. But the patient's prognosis was unfavourable with death after 2 weeks postoperatively. Discussion. According to the literature, DM is associated with an increased risk of infection and the development of IE. Patients with DM have an increased severity of IE and a high in-hospital mortality rate. Medium and long-term clinical outcomes, especially in patients with heart valvular surgery, reveal that in DM the diagnosis is established late, often progresses to embolic complications and recurrent infections and ends with an unfavourable prognosis. Conclusion. Nosocomial IE of prosthesis in patients with DM leads to severe complications and increases the death rate and the recurrences of IE. The peculiarity of this case is that the patient with DM after 11 after the AoV prosthesis develops a recurrence of IE complicated by valvular abscess and despite proper treatment dies.