Preserving confidentiality is problematic for human service practitioners if they know that a client is seriously harming a third party or could do so in the future. The present study concerned financial harm, as generated by gambling-related theft. Clients who disclose gambling-related theft potentially create a dilemma for practitioners, who may need to consider whether they have a professional duty to warn or in other ways protect third parties who are identifiable but uninvolved in treatment. Study participants included specialist gambling counsellors, practitioners working in agencies likely to attract clients with gambling problems and students in training. Data was collected by means of an online survey. Findings reveal how practitioners construe their profession's legal and ethical obligations when clients admit to gambling-related theft and when they personally believe that disclosure is warranted. Areas of uncertainty and disagreement have import for employing agencies, professional associations and tertiary training institutions.