Pyelonephritis is a bacterial inflammation of the kidneys and its pelvis. The disease can be acute or chronic. The causes are bacteria residing the mucosa of colon. They reach kidneys by blood or lymph way. Conductive factors are gravidity, renal and pelvis calculi, diabetes, chronic intestinal disease, traumas. Acute pyelonephritis appears suddenly, with fever, the temperature of body is becoming about 40oC, and profusely perspiration. He fever is accompanied with nausea, vomiting, lumbar, muscle and joint pain. Urine is becoming thick and there are many bacteria, leucocytes and sometimes blood. Children's pyelonephritis is violent and very heavy, with seizures and convulsions. Elderly persons have lighter symptoms of acute pyelonephritis. Chronic pyelonephritis is characterized with a lumbar dull pain an headache, increasing of the arterial blood pressure, presence of albumin, leucocytes and bacteria in the urine. The progress of the disease is undulating with exacerbations and amelioration.