Chronic pain is a prevalent condition in youth, and the pain experience is strongly influenced by emotional processes. Studying emotion variability and regulation (ER) may help better understand pain behavior. As the development of emotion-related abilities predominantly takes place in the family context, examining ER within parent-adolescent dyads is important. We set out to test the association of parent and adolescent ER, and adolescent emotional variability with adolescent pain behavior (i.e., pain interference, activity avoidance, activity engagement). A sample of 56 adolescents (Mage = 14.5, 85.7% female) with chronic pain and one of their parents (92.9% mothers) participated in this study. Adolescents completed baseline measures of average pain intensity, ER, and mean positive and negative affect. Further, adolescents completed an electronic diary for 14 consecutive days, reporting on emotional state, activity avoidance, activity engagement, and pain interference. Parents completed measures of ER and their own history of pain. We carried out a variable selection procedure, the least absolute shrinkage and selection operator (LASSO) method, to determine important predictors of adolescent pain behavior. Adolescent high positive affect ACCEPTED 3 was associated with more activity engagement, less pain interference and less activity avoidance, indicating that positive affect might enhance the willingness to engage in activities in the presence of pain. Adolescent ER strategy emotional reappraisal and parents’ own history of pain were predictors of less activity engagement. Parent ER was not related to adolescent ER. In conclusion, our results highlight the potential of enhancing positive affect as an intervention target for chronic pain.