BACKGROUND As pediatric ambulatory surgeries are rising and existing methods to reduce perioperative anxiety and pain are lacking in this population, a serious game for health (SGH), CliniPup, was developed to address this unmet need. CliniPup was generated using the SERES framework for serious game development. OBJECTIVE To clinically evaluate CliniPup, an SGH, as an adjunct therapy to existing pharmacological interventions aimed at reducing perioperative anxiety and pain in children undergoing ambulatory surgery. METHODS CliniPup was evaluated in a prospective, randomized, controlled pilot trial in 20 children aged 6-10 years who underwent elective surgery, and their parents. Study participants were randomly assigned to the test (n=12) or control group (n=8). Children in the test group played CliniPup 2-days prior to surgery and children in the control group received standard of care. On the day of surgery, pediatric anxiety was measured with the modified Yale Preoperative Anxiety Scale (mYPAS) and parental anxiety was assessed with the State-Trait Anxiety Inventory (STAI). Pediatric postoperative pain was assessed by the Wong-Baker Faces Pain Rating Scale (WBFPRS). Child and parent user experience and satisfaction was also evaluated in the test group using structured questionnaires. RESULTS Despite the small sample, preoperative anxiety scores were significantly lower (P = .01) in children who played CliniPup prior to surgery, compared to controls. Parental preoperative anxiety scores were also lower in the test group (P = .10), but did not reach significance. No significant differences were observed in postoperative pain scores between groups (P = .54). The evaluation of user experience and satisfaction revealed that both children and parents were satisfied with CliniPup and would recommend the game to peers. CONCLUSIONS Results of the pilot trial introduce CliniPup as a potentially effective and attractive adjunct therapy, to reduce preoperative anxiety in children undergoing ambulatory surgery, with a trend towards positive impact on parental preoperative anxiety. These results support the use of the SERES framework to generate an evidence-based SGH, which results in positive health outcomes for patients. Based on these preliminary findings, we propose a research agenda to further develop and investigate this tool.