This study investigates whether individualized, anticipatory temperament guidance could benefit the parent-child relationship and improve children's mental health over time. Parents of preschoolers in a health management organization completed a temperament questionnaire, received written parenting information tailored to their child's temperament, and were asked to complete a program evaluation questionnaire. The numbers of subsequent visits to the pediatric and psychiatry departments with anxiety, depression, attention deficit hyperactivity disorder, and other externalizing behavior diagnoses were compared over 15 years to a control sample that received only standard care. Parents positively reviewed the program and boys who received the intervention had fewer visits with psychiatric diagnoses. Analyses revealed an interaction effect, where boys with harder-to-manage temperaments saw a greater reduction in visits from the intervention. By sensitizing parents to their child's temperament and helping parents understand and manage temperament-related behaviors, anticipatory guidance can encourage a positive parent-child relationship and reduce future occurrences of psychiatric diagnoses.