Methicillin-resistant S. aureus (MRSA) is one of the major causes of nosocomial infections worldwide and the prevalence of MRSA in Italy is one of the highest in Europe. More recently MRSA has also emerged as an agent of community invasive infections. CA-MRSA (community associated MRSA) has a typical antibiotics susceptibility pattern and it is responsible for skin and soft tissues infections, especially in young healthy individuals. In the reported case, a 17 years-old boy, without any previous contacts with healthcare facilities, developed sepsis with functional impairment of right leg after an intramuscular injection received at home. MRSA not susceptible to clindamycin and erythromycin was isolated from blood cultures. Despite adequate antibiotic therapy, the patient still complained of leg dysfunction and pain. Several imaging investigations were performed but only a pelvic magnetic resonance was able to show an acute sacrum-ileitis, with a voluminous abscess between ileus-psoas muscle and right emi-sacrum. The patient experienced clinical improvement only after the combination of the abscess’ drainage with adequate antibiotic therapy. Our patient developed a serious infection caused by a peculiar community-acquired MRSA, in absence of clear risk factors. For this reason, in absence of clinical response to antibiotic therapy, it’s mandatory to suspect a multi-resistance bacterial infection in order to begin as quickly as possible the most appropriate therapy and improve prognosis.