A 72-year-old man presented with pain and swelling in the penis, indicating penile infection or abscess. An ultrasound was performed but unable to lead to a diagnosis of abscess. Magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) was strongly suggestive of penile abscess. The puncture of the abscess was unsuccessful. However, pus was drained spontaneously via the urethra, and the symptoms disappeared eventually. Although ultrasound can be useful, sometimes it might be difficult to distinguish between inflammatory tissue and abscess containing necrotic tissue. MRI, especially DWI, can be a powerful tool for diagnosing abscess in the penis.