OBJECTIVE: To explore the acceptability of implementing an online tool for the assessment and management of childhood obesity (Computer-Assisted Treatment of CHildren, CATCH) in primary care. DESIGN AND SETTING: An uncontrolled pilot study with integral process evaluation conducted at three general practices in northwest London, UK (November 2012-April 2013). PARTICIPANTS: Families with concerns about excess weight in a child aged 5-18 years (n=14 children). INTERVENTION: Families had a consultation with a doctor or nurse using CATCH, which assessed child weight status, cardiometabolic risk and risk of emotional and behavioural difficulties and provided personalised lifestyle advice. Families and practitioners completed questionnaires to assess the acceptability and usefulness of the consultation, and participated in semistructured interviews which explored user experiences. OUTCOME MEASURES: The primary outcome was family satisfaction with the tool-assisted consultation. Secondary outcomes were practitioners' satisfaction, and acceptability and usefulness of the intervention to families and practitioners. RESULTS: The majority of families (86%, n=12) and all practitioners (n=4) were satisfied with the consultation. Participants reported that the tool was easy to use, the personalised lifestyle advice useful and the use of visual aids beneficial. Families and practitioners identified a need for practical, structured support for weight management following the consultation. CONCLUSIONS: The results of this pilot study indicate that an online tool for assessment and management of childhood obesity can be implemented in primary care, and is acceptable to patients, families and practitioners. Further development and evaluation of the tool is warranted.