This study determined if the generalized equations created for the Rockport Fitness Walking Test were a valid estimation of cardiorespiratory fitness for adults with mental retardation (MR). Subjects included 25 males and females (X age = 33.3 ± 7.4 yr) with MR. A maximal treadmill test was administered (X VO2peak = 29.5 ± 7.2 ml • kg-1’min-1; 2.2 ± 0.62 1 • min-1). Subjects’ age, weight, sex, walk time, and immediate post-HR were used in the generalized equations for predicting VO2peak (X VO2peak = 36.5 ± 7.6 ml • kg-1 • min-1 and 2.7 ± 0.66 1 • min-1). Significant correlations (P < 0.01) were obtained between the measured and predicted peak VO2 levels. However, significant and consistent differences were also observed between the measured and predicted VO2peak values (P < 0.02). Only 28% (1•min-1) and 36% (ml•kg-1•min-1) of the subjects’ measured VO2peak fell within the prespecified value of the predicted VO2peak, thus indicating that the prediction equations overestimated the VO2peak and cardiovascular fitness levels of adults with MR. © 1994 by the American College of Sports Medicine.