OBJECTIVE The purpose of our study was to describe the MR features of testicular adrenal rest tissue in patients with congenital adrenal hyperplasia and to compare the usefulness of MR imaging with that of sonography for the detection of testicular adrenal rest tissue. METHODS Nineteen patients with congenital adrenal hyperplasia underwent MR imaging and gray-scale and color Doppler sonography of the testicles during the same visit to our institution. Findings were compared. RESULTS MR features of testicular adrenal rest tissue included the following: isointensity (71% of the masses) and slight hyperintensity (29% of the masses) relative to normal testicular tissue on T1-weighted images; hypointensity relative to normal testicular tissue on T2-weighted images (100% of the masses); and diffuse enhancement on contrast-enhanced T1-weighted images (85% of the masses). MR imaging and sonography revealed the testicular lesions equally well. Eleven (58%) of 19 patients had normal findings on MR imaging and sonography. Eight (42%) of 19 patients had 14 intratesticular masses detected by both imaging techniques. CONCLUSIONS MR imaging and sonography are equally useful in the detection of testicular adrenal rest tissue. Because sonography is more accessible to most institutions and is less expensive, it is the imaging technique of choice for the detection of testicular adrenal rest tissue.