Infective endocarditis (IE) caused by Gram-negative bacteria is a rare and insufficiently characterized form of endocarditis. The literature review presents data on the frequency, course, risk factors, diagnosis and treatment of both IE caused by the HACEK microorganisms (Haemophilus spр., Aggregatibacter spp., Cardiobacterium hominis, Eikenella corrodens, Kingella) and other Gram-negative bacteria. Gram-negative bacteria are the cause of 3.6–13.6 % IE cases (HACEK microorganisms in 0.8–3 % of IE cases in adults, non-HACEK in 1.8–3.9 %). Patients with IE caused by the HACEK microorganisms are younger, their disease is not associated with previous in-hospital treatment and is subacute with favorable prognosis (intrahospital mortality is 2–3 %). HACEK microorganisms mostly retain sensitivity to many antibiotics. Risk factors of IE caused by HACEK microorganisms are dental interventions, heart disorders, valve prostheses and other implanted cardiac devices. IE caused by non-HACEK Gram-negative bacteria is more common in elderly with concomitant disorders and usually is acute; intrahospital mortality is 13–36.5 %. Risk factors of IE caused by non-HACEK microorganisms are valve prostheses, electrical pacemakers, venous and central catheters, recent in-hospital treatment, Gram-negative bacteremia, decreased immunity, drug abuse, urinary infection, alcoholism, cirrhosis of the liver, removed spleen, consequences of dog and cat bites, working with the soil. Among Gram-negative non-HACEK bacteria causing IE, 28 % have multi-drug resistance (MDR / XDR) against antibiotics. Therefore, Gram-negative bacteria rarely cause IE but during selection of empiric therapy in patients with IE with corresponding risk factors, probability of Gram-negative causative microorganisms in IE etiology should be taken into account.