Acute septic arthritis is a common diagnosis usually seen by radiologists, internists, and family physicians; it is most commonly caused by pyogenic pathogens. In the majority of patients, it is possible to identify, the infection mechanism: spread of infection can be due to hematogenous dissemination, a contiguous source of infection, direct inoculation, or surgical contamination. Radiologic findings include increase in articular space and central and marginal bone erosions; the first plain radiograph changes are seen 8-10 days after symptoms. We present the case of a 9-year-old girl with septic arthritis of right hip; in presenting this case we offer a brief summary of clinical features and main imaging findings of septic arthritis (plain radiographs, ultrasonography, and gammagraphy).