We report a 62-year-old woman with a locked-in syndrome with bilateral masticatory spasms and persistent trismus, who was still able to yawn. A vascular malformation of the basilar artery-megadolichobasilar artery (fusiform aneurysm, vertebrobasilar dolichoectasia) was determined to be the underlying cause of this rare combination of symptoms. A thrombus in the megadolichobasilaris as well as an almost total pontine infarction were demonstrated on CT- and MRI-scans. Thus, trismus may be associated with locked-in syndrome due to megadolichobasilar artery thrombus, although yawning is still possible.