Urinary tract infections refer as inflammations of any part of the urinary tract and cover various diseases and clinical syndromes. Urinary tract infections are the second most occurring infections, after respiratory infections, and due to their high rate, they are regarded as huge public health issue. Most infections are of bacterial etiology and they are the result of a complex interaction between the causative agent and local or systemic immune response factors. Acute pyelonephritis belongs to the upper urinary tract infections and refers to the kidney parenchyma and renal pelvis inflammation. Same as other urinary tract inflammations, acute nephritis is predominantly of bacterial etiology and ascending pathway is the dominant pathwayof causative agent’s spreading from lower urinary tract. Acute pyelonephritis can manifest itself in various symptoms while the typical ones are increased body temperature, chills, shivering, vomiting, lumbar pain and patient’s generally ill condition. With such manifestation of the inflammation, it is relatively easy to make a working diagnosis and to confirm the inflammation, though special attention should be paid to inflammations with children and elderly people with co-morbidities. Comprehensive diagnostics is not necessary while antimicrobial treatment needs to be conducted with all patients because of numerous possible complications. Due to good kidney vascularization, there is a significant danger for the causative agent to spread into blood thus causing sepsis or septic shock. Beside present antimicrobial treatment, numerous scientist all over the world are working on understanding the inflammatory processes and are studying the conduction of antioxidative therapy in the inflammatory and oxidative stress conditions.