Abstract. Despite the burgeoning use of respiratory sinus arrhythmia (RSA), heart period (HP), and blood pressure (BP) to study individual differences in autonomic regulatory processes in young adults, few studies have examined the short-term reliability of such autonomic measures in emerging adulthood. If resting autonomic measures indeed reflect “trait-like” individual differences, they should have acceptable levels of test-retest reliability. We examined the 1-month test-retest reliability of resting measures of RSA as well as HP, systolic (SBP) and diastolic blood pressure (DBP) in a sample of 41 healthy young adults. Test-retest reliability of all four measures was good-to-excellent across the 1-month period. However, uncontrolled mean RSA declined from Time 1 to Time 2, suggesting that while individual differences in RSA were stable, mean RSA appeared to be sensitive to condition effects. Even with random variation, all of these measures were stable across one month, demonstrating acceptable short-term test-retest reliability in emerging adulthood.