The present paper demonstrates that mental rotation as used in the processing of disoriented objects (Cooper and Shepard 1973) can also be used as an explanatory concept for the processing of perspective problems in which the task is to imagine how an environment will appear from another vantage point. In a cognitive map, subjects imagined an initial line of vision and subsequently processed a reorientation stimulus, requesting them to imagine a turn over 0, 45, 90, 135, or 180 degrees. Time for a reorientation increased linearly with the size of the imaginary turn up to 135 degrees and decreased for turns of 180 degrees; apparently, about-faces were relatively easy to imagine. The increment of reorientation time between 0 and 135 degrees was larger for maps presented in unfamiliar orientations such as South-West up. Both the increment and the interaction with familiarity are consistent with an explanation in terms of mental rotation.