A 39-year-old woman arrived to the emergency department complaining of a constant, progressive, left flank pain, with no beneficial effect from spasmolytic and nonsteroidal antiinflammatory drugs. Two years before, she suffered another episode of right flank pain and stranguria, but instrumental examinations (ultrasonography, urography) remained negative. Besides a mild tenderness in the left flank, physical examination was normal. Blood chemistry panel showed leukocytosis (17.2 x 10(3) mL, neutrophils 82.8%) and a slight increase of serum lactate dehydrogenase (LDH) (543 U/L versus 230 to 460 U/L). Urinanalysis showed a slight hemoglobinuria (0.5 mg/dL), and sediment contained some red cells and leukocytes. Diagnostic examinations (ultrasonography, computed tomography) showed a left renal nonhomogeneous space-occupying lesion, orientative for renal malignancy. She was transferred to the urology department and operated. Both intraoperatory and histological diagnosis was ischemic infarction and, after exclusion of all possible underlying causes, final diagnosis was idiopathic renal infarction. Diagnostic procedures and literature reports are discussed.