PURPOSE: To evaluate the characteristics of magnetic resonance (MR) images in Peyronie's disease and to assess the usefulness of post-erection penile MRI. MATERIALS AND METHODS: We retrospectively reviewed the MR images of seven patients in whom Peyronie's disease was clinically suspected. All seven underwent pre- and post-erectile MRI. After the aquisition of erectile MRI, three patients also underwent contrast-enhanced MRI. We compared image quality and the rate of detection of penile plaque between pre-erectile and post-erectile images. In three patients who underwent contrast- enhanced MRI, we assessed correlation between the contrast enhancement pattern, as seen on MRI, of the plaque and corpus cavernosa and clinical inflammatory signs such as painful erection. RESULTS: In the seven patients, all post-erectile MRI images showed localized thickening and irregularities of the tunica albuginea and the septum penis, suggesting penile plaque. On pre-erectile MRI, however, plaque was detected in five cases. In six of seven cases, plaque as seen on T2-weighted images (T2WI) showed low signal intensity similar to that of the tunica albuginea, and as seen on T1-weighted images (T1W1), a signal intensity of signal intensity similar to or similar to or slightly higher than that of the tunica albuginea. In one case, plaque showed high signal intensity on both T1WI and T2WI. On T1WI, the corpus cavernosa showed homogeneous medium-signal intensity on all pre- and post-erectile MR images. On pre-erectile T2WI, the corpus cavernosa of six patients showed heterogeneous high signal intensity, whereas on post-erectile T2WI the corpus cavernosa of all patients showed homogeneous high signal intensity. Due to the enlarged penis and homogeneous signal intensity of the corpus cavernosa, the image quality of post-erectile images was superior to that of pre-erectile imjages. The images of two of three patients who underwent contrast enhanced MRI showed strong enhancement of the plaque and adjacent corpus cavernosa, while in one case, no enhancement was noted. Independently of the enhancement pattern, these three patients had no active inflammatory clinical signs such as painful erection. CONCLUSION: In Peyronie's disease, all plaque is clearly, visualized on MRI. In terms of image quality and plaque detection, post-erectile penile MR imaging is superiou to pre-erectile imaging.