Early childhood environment is critical to subsequent physical health in children and is influenced by children's primary caregivers \u2014 typically mothers. Maternal stress, one aspect of a child's environment, may shape the functioning of the child's physiological stress response system, which has been linked to later health outcomes, including pain. The current study evaluated whether: 1) early maternal stress, defined as maternal depressive symptoms and low socio-economic status, predicts later child pain; 2) early maternal stress relates to later child daily cortisol output; and 3) child's cortisol output across the day mediates the relation between early maternal stress and child pain. Maternal stress was assessed via questionnaires at twin age 12-months. At twin age seven years, twins' salivary cortisol was collected three times per day for three days. At twin age nine years, twins rated how often they experienced stomach, headache, and back pain weekly or more frequently. Results of multilevel linear and logistic regression analyses showed that early maternal stress did not predict later children's daily cortisol output or extent of child pain. Therefore, findings were inconsistent with the proposed mediation model. However, there was a marginally significant negative relation between child daily cortisol output and later extent of child pain. Current findings suggest that functioning of the stress response system, reflected in cortisol output, may have implications for the development of child pain. Future work evaluating intensely stressful early environments may provide clues about the links between a child's early environment and the development of his/her stress response system.