Spatial ability is an important factor in learning anatomy. Students with high scores on a mental rotation test (MRT) systematically score higher on anatomy examinations. This study aims to investigate if learning anatomy also oppositely improves the MRT-score. Five hundred first year students of medicine ("n" = 242, intervention) and educational sciences ("n" = 258, control) participated in a pretest and posttest MRT, 1 month apart. During this month, the intervention group studied anatomy and the control group studied research methods for the social sciences. In the pretest, the intervention group scored 14.40 (SD: plus or minus 3.37) and the control group 13.17 (SD: plus or minus 3.36) on a scale of 20, which is a significant difference ("t"-test, "t" = 4.07, df = 498, P less than 0.001). Both groups show an improvement on the posttest compared to the pretest (paired samples "t"-test, "t" = 12.21/14.71, df = 257/241, "P" less than 0.001). The improvement in the intervention group is significantly higher (ANCOVA, "F" = 16.59, df = 1;497, "P" less than 0.001). It is concluded that (1) medical students studying anatomy show greater improvement between two consecutive MRTs than educational science students; (2) medical students have a higher spatial ability than educational sciences students; and (3) if a MRT is repeated there seems to be a test effect. It is concluded that spatial ability may be trained by studying anatomy. The overarching message for anatomy teachers is that a good spatial ability is beneficial for learning anatomy and learning anatomy may be beneficial for students' spatial ability. This reciprocal advantage implies that challenging students on spatial aspects of anatomical knowledge could have a twofold effect on their learning. (Contains 1 table.)