Because of the similarity between the diagnostic criteria for acute rheumatic fever (ARF) and post-streptococcal reactive arthritis (PSRA), therefore diagnosis and treatment of PSRA are not well defined. To clarify whether PSRA is a separate disease entity? And to evaluate the extent of joint affection by using various clinical, laboratory and radiological tools. Fifty patients with arthritis secondary to infection with Group A ß-haemolytic streptococcus (GAβS) attended Outpatient Rheumatology Clinics of Rheumatology and Rehabilitation and Internal Medicine Departments; Assuit University Hospitals, in addition to 20 healthy volunteers as controls were included in this study. All patients were submitted to complete medical history and clinical examination. Erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), Rheumatoid factor (RF), Antinuclear antibody (ANA), throat swab, Anti-streptolycin-O titre (ASOT), Electrocardiography (ECG) and Echocardiography have been done to all patients. Plain radiography, ultrasonography (US) and Magnetic Resonance Imaging (MRI) to both knees and ankles were done to all patients. ASOT was positive with a range (200-800) IU. Culture of throat swab was positive for GAßS in 72%, staphylococci in 24% and pneumococci in 16% of the patients. All patients had non migratory arthritis of lower limbs. Knees and ankles synovitis with minimal effusion was detected in 36% of the patients by US, and 32% and 40% by MRI respectively. Synovitis with marked effusion of knees and ankles was detected in 36% and 44% of patients respectively by US and 40% by MRI. In conclusion, PSRA is a separate disease entity. The extent of joint affection might be evaluated by the use of US and MRI as the findings were concordant in knee joint affection. MRI was preferable in evaluating ankle joint synovitis.