Purpose: To investigate the clinical characteristics and magnetic resonance imaging (MRI) findings of the extraocular muscle and ocular motor nerves in congenital monocular strabismus fixus. Methods: The retrospective observational case series of three patients with congenital monocular strabismus fixus were reviewed between January 1, 2006, and December 31, 2016. Ophthalmologic examination and thin-sectioned MRI of the ocular motor nerve and the orbit were performed on the three patients. Results: Three patients presented with unilateral non-progressive strabismus fixus with marked limitations of movement in all directions since birth. Of the three patients, one presented with esotropia, one with a large degree of exotropia and hypertropia, and one with an almost normal primary position. All three patients had normal ocular motor nerves, but adherences among the extraocular muscles, posterior Tenon's capsule, and the globe within the muscle cone on MRI. Two patients underwent strabismus surgery, but there were no postoperative improvements in the primary position and eye movements. Conclusions: Extensive adherences among the extraocular muscles, posterior Tenon's capsule, and globe may partially explain the cause of congenital monocular strabismus fixus and why strabismus surgery was ineffective. The findings further highlight the importance of MRI in detecting and characterizing atypical forms of strabismus.