Background. Physical activity has been considered to be a socially desirable behavior that might be overreported because of a social desirability bias. This study involved an examination of the possible influence of social desirability on self-report measures of physical activity. Methods. Participants were male and female college students (N = 782) who completed the Lie scale of the Eysenck Personality Questionnaire (L-scale), Marlowe-Crowne Social Desirability Scale (SDS), Godin Leisure-Time Exercise Questionnaire (GLTEQ), and Stanford Usual Activity Questionnaire. Results. Scores from the Lie scale were not significantly correlated with scores from either the Godin Leisure-Time Exercise Questionnaire or the Stanford Usual Activity Questionnaire. With the Social Desirability Scale, there were statistically significant, but weak correlations with scores from the Godin Leisure-Time Exercise Questionnaire and the Stanford Usual Activity Questionnaire. There was no influence of the Lie scale and Social Desirability Scale on the magnitude of the correlations between scores from the two measures of physical activity. Conclusions. This study provides minimal evidence of an influence of social desirability on scores from two self-report instruments for measuring physical activity in young adults. © 2004 Elsevier Inc. All rights reserved.