Many transformations that occur in adolescence are related to emotion and emotion regulation, yet very little is known about the autonomic underpinnings of these changes. The aim of the study was to document age-related differences in autonomic responses to social stress and relations to emotion regulation. Ninety-nine female adolescents engaged in a paced breathing and a spontaneous speech task while electrocardiography measurements were taken. Spectral decomposition of the heart period data was used to create measures of sympathetic and parasympathetic activity. Results revealed a positive correlation between age and sympathetic activity and a negative correlation between age and parasympathetic activity. These findings contribute to a better understanding of the age-related norms of cardiac variability across adolescence. © 2011 Wiley Periodicals, Inc. Dev Psychobiol 54:207-214, 2012.