Background: Adolescence is characterized by profound changes in physical, psychological, and social functioning thought to be accompanied by intense and varying moods. Purpose: Within a psychophysiological framework, this study examined the prevalence of 12 self-reported mood states of adolescents; investigated associations between specific mood states and ambulatory blood pressure readings; and explored effects of interactions among moods, gender, ethnic group, and maturation on ambulatory blood pressures. Methods: The sample included 371 African American, European American, and Hispanic American adolescents 11 to 16 years old. Systolic (SBP) and diastolic (DBP) blood pressures were measured every 30 min with an ambulatory monitor and were synchronized with electronic activity monitoring and moods self-recorded during waking hours in a checklist diary. Results: Moods differed significantly by gender, ethnic group, and maturation. Controlling for height, maturation, gender, ethnic group, mother's education, position, location, activity, other moods, and interactions of moods with other variables in a multilevel, random coefficients regression model, both positive and negative mood states were associated with higher levels of SBP and DBP; being relaxed or bored, or having a feeling of accomplishing things were associated with lower SBP and DBP. There were significant interaction effects of moods with physical maturity, gender, and ethnic group on ambulatory SBP and DBP. Conclusions: Further study of the modifying effects of gender, ethnic group, and stage of development on reports of moods, and their associations with cardiovascular responses is recommended.