This review discusses the various gross and histologic findings seen in renal infections due to bacteria, viruses, fungi, and mycobacteria. It is crucially important to separate infectious processes in the kidney from other inflammatory or neoplastic processes, as this will have a major impact on therapy. We describe the diagnostic features of renal infections with a specific focus on the differential diagnosis and other processes that may mimic infection. The topics discussed include acute bacterial pyelonephritis, chronic bacterial pyelonephritis, xanthogranulomatous pyelonephritis, malacoplakia, viral infections in the kidney, fungal pyelonephritis and mycobacterial infection of the kidney.