BACKGROUND: While biological and behavioral stress response systems are intact in early gestation, preterm infants\' behaviors are often more subtle and difficult to interpret compared with full-term infants. They are also more vulnerable for regulatory issues (ie, colic) that are known to impact caregiver-infant interactions. Biobehavioral measures such as behavioral responsivity and heart rate variability (HRV), particularly cardiac vagal tone, may help elucidate preterm infants\' stress/regulatory systems. PURPOSE: To test the hypotheses that preterm infants\' consoling behaviors and high-frequency (HF) HRV in the first week of life are significantly associated and they are inverse correlates of future colic risk. METHODS/SEARCH STRATEGY: Thirty preterm (mean +/- SE = 32.7 +/- 0.3 weeks postmenstrual age [PMA]) infants underwent direct NIDCAP (Newborn Individualized Development and Assessment Program) observation during routine care and had HRV measurements during their first week postbirth. Sixty-three percent of mothers completed the Infant Colic Scale at 6 to 8 weeks adjusted postnatal age. Nonparametric tests were used to determine associations among behaviors, HRV, and maternal perceptions of infant colic. FINDINGS/RESULTS: Self-consoling behaviors were positively associated with HF-HRV (vagal tone). In addition, stress behaviors were positively associated with low-frequency/high-frequency HRV (sympathetic dominance). Infants who displayed more stress behaviors also demonstrated more self-consoling behaviors. No significant associations were found with colic. IMPLICATIONS FOR PRACTICE: HF-HRV provides information on the infant\'s capacity to modulate stress and is a useful, noninvasive measure when behaviors are more difficult to discern. IMPLICATIONS FOR RESEARCH: Further study in a larger sample is needed to determine whether behavioral stress measures and HF-HRV may be useful to determine colic risk.