OBJECTIVE: (1) To present the magnetic resonance imaging (MRI) findings of congenital muscular torticollis (CMT) of subjects who underwent surgical release and subjects who showed a good prognosis with stretching exercises and (2) to correlate the MRI findings with the histopathologic findings of CMT for subjects who underwent surgical release in order to examine the hypothesis that the MRI findings of CMT can be used as a determinant to perform surgical release of CMT. METHOD: The neck MRI findings of 33 subjects who underwent surgical release for CMT were compared with those of 18 subjects who were successfully managed only with conservative management. The MRI findings were correlated with the histopathologic sections of the CMT mass. RESULTS: All 33 subjects (100%) who underwent surgical release showed one or more low signal intensities within the involved sternocleidomastoid muscle (SCM) on the T1- and T2-weighted images of neck MRI. The eighteen non-surgical candidates showed only enlargement of the SCM without low signal intensity within the SCM. The histopathologic findings showed interstitial fibrosis and/or the presence of aberrant tendon-like excessive dense connective tissue that was either well-arranged or disorganized. CONCLUSION: The histopathologic findings and MRI findings showed good correlation in terms of the amount of fibrosis and aberrant dense connective tissue within the SCM. If multiple or large low signal intensities within the SCM are noted, we think that surgical release should be considered.