A 2.5-year-old girl, previously healthy, was admitted to the hospital because of the respiratory tract infection and erythema multiforme. On physical examination, petechiae and polymorphic rash with changes, 0.5 to 10 cm in diameter on buttocks, legs and feet were found (Fig. 1). Laboratory tests revealed increased inflammatory markers: CRP - 1.3 mg/dl (Normal value < 1.0 mg/dl), leukocytosis - 11.7 x 103/ul, ESR - 16 mm/1 h and IgA - 164 mg/dl (Normal value: 15-154). Urinalysis and serum creatinine (0.3 mg/dl) were normal. The girl received amoxicillin with clavulanic acid (90 mg/kg/day) for 7 days. After 5 days of treatment, inflammatory markers resolved, but because of recurrent skin changes, another etiology of the infection was suspected. Laboratory tests excluded tuberculosis, streptococcal infection, yersiniosis, toxoplasmosis, lambliasis, borreliosis, EBV and HSV infections. Mycoplasma pneumoniae infection was confirmed by a positive serological test (Table 1). Indication for the X-ray was the positive titer of antibodies against M. pneumoniae. X-ray of the chest revealed right-sided pneumonia without any changes on auscultation of the lungs. Treatment with clarithromycin at a dose of 15 mg/kg/day was started and was continued for 21 days. After 3 weeks of treatment, skin changes disappeared and the chest X-ray image was normal.