The purpose of this study was to develop a regression equation to predict maximal oxygen uptake (VO[subscript 2]max) based on nonexercise (N-EX) data. All participants (N = 100), ages 18-65 years, successfully completed a maximal graded exercise test (GXT) to assess VO[subscript 2]max (M = 39.96 mL[middle dot]kg[superscript -1][middle dot]min[superscript -1], SD = 9.54). The N-EX data collected just before the maximal GXT included the participant's age; gender; body mass index (BMI); perceived functional ability (PFA) to walk, jog, or run given distances; and current physical activity (PA-R) level. Multiple linear regression generated the following N-EX prediction equation (R = 0.93, SEE = 3.45 mL[middle dot]kg[superscript -1][middle dot]min[superscript -1], % SEE = 8.62): VO[subscript 2]max (mL[middle dot]kg[superscript -1][middle dot]min[superscript -1]) = 48.0730 + (6.1779 x gender; women = 0, men = 1) - (0.2463 x age) - (0.6186 x BMI) + (0.7115 x PFA) + (0.6709 x PA-R). Cross validation using PRESS (predicted residual sum of squares) statistics revealed minimal shrinkage (R[subscript p] = 0.91 and SEE[subscript p] = 3.63 mL[middle dot]kg[superscript -1][middle dot]min[superscript -1]); thus, this model should yield acceptable accuracy when applied to an independent sample of adults (ages 18-65 years) with a similar cardiorespiratory fitness level. Based on standardized Beta-weights, the PFA variable (0.41) was the most effective at predicting VO[subscript 2]max followed by age (-0.34), gender (0.33), BMI (-0.27), and PA-R (0.16). This study provides a N-EX regression model that yields relatively accurate results and is a convenient way to predict VO[subscript 2]max in adult men and women. (Contains 3 tables and 2 figures.)