Several investigators have used meta-analysis to compare the results of studies of gender differences on various spatial tests and have concluded that the magnitude of the gender difference in spatial ability is decreasing over time. The present study used meta-analytic techniques to compare the effect size (d) of the gender difference in 14 studies published from 1975 to 1992 which administered the Mental Rotations test to adolescents and young adults. Males scored significantly higher than females in all the studies. Analyses of the d's computed for the studies revealed that the magnitude of the gender difference on the Mental Rotations test has remained stable over time. Neither the Pearson correlation relating the d's to the publication dates of the studies nor the Z test of the linear contrast relating the publication dates of the studies to the effect sizes showed a linear change in the size of the gender difference over time. The finding of a stable gender difference on the Mental Rotations test argues against the general conclusion that the gender difference in spatial ability is decreasing.