Background: Attention-deficit/hyperactivity disorder (ADHD) develops in early childhood and carries lifelong impact, but early identification and intervention ensure optimal clinical outcomes. Prolonged or excessive parenting stress may be a response to infant behavioral differences antecedent to developmental disorders such as ADHD, and therefore represents a potentially valuable inclusion in routine early-life assessment. To investigate the feasibility of using routinely-collected self-reported maternal parenting stress as a risk marker for child ADHD, this study investigated the longitudinal association between maternal parenting stress from 1 to 36 months after childbirth and child ADHD in early adolescence. Methods: The sample comprised 2,638 children (1,253 girls) from the Tokyo Teen Cohort population-based birth cohort study. Mothers recorded parenting stress five times from 1 to 36 months following childbirth in the Maternal and Child Health Handbook, a tool used for routine early-life assessment in Japan. Nine years later, mothers evaluated their child's ADHD symptoms at 12 y using the hyperactivity/inattention subscale from the Strength and Difficulties Questionnaire. Results: Approximately 7.5% of parents reported that they had parenting stress at 36 m after childbirth. 6.2% of children were evaluated as above the cut-off for ADHD symptoms at 12 y. Parenting stress at 1 and 3-4 m was not associated with child ADHD symptoms at 12 y. However, child ADHD symptoms at 12 y was significantly associated with parenting stress at 9-10 m (unadjusted OR = 1.42, p =.047, 95% CI [1.00, 2/00]), 18 m (unadjusted OR = 1.57, p =.007, 95% CI [1.13, 2.19]) and 36 m (unadjusted OR = 1.67, p =.002, 95% CI [1.20, 2.31]). These associations remained after adjustment for child's sex, age in months and family income. Conclusions: We identified associations between parenting stress at 9-10, 18 and 36 m after childbirth and child ADHD symptoms at 12 years old. Self-reported parenting stress data may have utility as an early indicator for ADHD risk. Participation in early-life health checks, assessment of parenting stress, and tailoring support to family needs should be promoted for early identification and intervention for ADHD.