&NA;Although head trauma is the leading cause of acquired trochlear nerve dysfunction, it receives little attention in the neurosurgical literature. A case is reported of closed head injury that resulted in a right superior oblique palsy in association with incoordination on the left side. Diagnostic imaging revealed a normal cranial computed tomographic scan and a left dorsal midbrain lesion on magnetic resonance imaging scan. The relevant anatomy is reviewed, as well as the action of the superior oblique muscle, its agonists and antagonists, and the clinical manifestations of superior oblique dysfunction. This case is one of the few we are aware of in which a relatively isolated trochlear nerve palsy is the result of a lesion that can be documented by diagnostic imaging, and the first in which the imaging modality is magnetic resonance imaging scan. (Neurosurgery25:978‐981, 1989)