Severe redness of the lips and mouth is a non-contagious disease with fever and rash as typical symptoms, mostly seen in children under 5 years of age. The disease is now attracting the attention of parents and medical professionals, as the number of cases continues to increase. To avoid a malignant situation, the disease should be detected and diagnosed early. What tests are needed for severe red congestion of the mouth and lips? Persistent fever, often with a body temperature of 39°C or higher. Bilateral conjunctival congestion, flushing of the mouth and lips with chapping or bleeding is common, and a prune-like tongue is seen. There is hard edema in the hands, early flushing of the palms and soles, and after 10 days, characteristic large flaky peeling of the ends of the toes, appearing at the skin junction of the nail bed. There is also acute nonsuppurative transient cervical lymph node swelling, most prominent in the anterior neck, about 1.5 cm or more in diameter, mostly appearing unilaterally, with slight tenderness, occurring within 3 days after the onset of fever and resolving spontaneously after a few days. Soon after the onset of fever (about 1-4 days), a maculopapular or erythema multiforme-like rash, or occasionally a prickly rash-like rash, mostly on the trunk, but without herpes and crusts, subsides in about a week. The patient’s pulse is accelerated, and tachycardia, gallop rhythm, and low heart sounds can be heard on auscultation. Systolic murmurs are also more frequently present. Echocardiography and coronary angiography may reveal coronary aneurysms, pericardial effusion, left ventricular enlargement, and mitral valve insufficiency in most patients. Occasionally, joint pain or swelling, cough, runny nose, abdominal pain, mild jaundice, or signs of aseptic encephalomyelitis may be seen. In the acute phase, about 20% of cases show flushing and desquamation of the perineum and perianal skin and reappear as erythema or crusting at the original site of BCG vaccination 1 to 3 years ago. In the recovery period, cross-groove spinning is seen on the nails. When the body temperature drops, membranous peeling of the finger and toe ends appears. After blood tests, the total white blood cell count and granulocyte percentage increase in the acute phase, and the nucleus shifts to the left. Mild anemia is seen in more than half of the patients. Blood sedimentation is significantly increased, up to 100 mm or more in the first hour. The serum protein fluorophoresis shows an increase in globulins, especially alpha and 2 globulins. IgG, IgA and IgA are elevated. Platelets start to increase in the second week. The blood is hypercoagulable. Anti-streptococcal hemolysin O titers were normal. Rheumatoid factor and antinucleosome are negative. c-reactive protein is increased. Serum complement is normal or slightly elevated. Urine sedimentation may show leukocytosis and/or proteinuria. The electrocardiogram may show a variety of changes, with ST-segment and T-wave abnormalities, as well as prolonged P-R and Q-R intervals, abnormal Q waves and rhythm disturbances. 2D echocardiography is suitable for cardiac examination and long-term follow-up in half of the cases to detect various cardiovascular pathologies such as pericardial effusion, left ventricular enlargement, mitral valve insufficiency and coronary artery dilatation or aneurysm formation. Preferably, weekly examinations during the acute and subacute phases of the disease are the most reliable non-invasive method of monitoring coronary aneurysms. In cases presenting with aseptic meningitis, lymphocytes in the cerebrospinal fluid may be as high as 50 to 70/mm3. In some cases, slightly high serum bilirubin or ghrelin may be seen. Bacterial culture and viral isolation are negative results.