INTRODUCTION AND AIMS: Clients in opioid substitution therapy often have considerable unmet health-care needs. The current study aimed to explore health problems related to opioid substitution therapy among clients on methadone and buprenorphine treatment. DESIGN AND METHODS: A self-complete, cross-sectional survey conducted among 508 patients receiving methadone and buprenorphine treatment at community pharmacies in New South Wales (NSW), Australia. RESULTS: The most common problems for which participants had ever sought help were dental (29.9%), constipation (25.0%) and headache (24.0%). The most common problems for which participants would currently like help were dental (41.1%), sweating (26.4%) and reduced sexual enjoyment (24.2%). There were no significant differences between those currently on methadone and those currently on buprenorphine for any of the health problems explored, nor differences for gender or treatment duration. Participants on methadone doses 100 mg or above were significantly more likely to want help currently for sedation. DISCUSSION AND CONCLUSIONS: The considerable unmet health care needs among participants in this study suggest that treatment providers should consider improving the detection and response to common health problems related to opioid substitution therapy.