Actinomycosis is a rare anaerobic bacterial infection of humans generally caused by Actinomyces israelii and other anaerobic filaments. Owing to slow growth over long periods of time, it usually presents as a mass lesion mimicking a tumor. Genitourinary actinomycosis is rare, and renal actinomycosis is often misdiagnosed as renal cancer. Diagnosis of actinomycosis mostly relies on demonstrating sulfur granules in pus or histologic analysis of a surgical specimen. Here, we present a case of actinomycosis of the kidney with the clinical presentation of acute emphysematous pyelonephritis.