This study aimed to develop a better understanding of the motives for suspected buprenorphine diversion during supervised dosing. Structured interviews were conducted with clients after 71 episodes of diversion at 3 opioid substitution treatment clinics in Sydney, Australia. Interviews were conducted by the clinic manager. An equivalent number of suspected episodes involved diversion via removal of buprenorphine from the mouth (n = 35), and secretion of buprenorphine in the mouth (n = 32). Denial of diversion occurred in 45% of suspected episodes and was significantly associated with secretion of buprenorphine in the mouth (P < .0001), suggesting a possible misunderstanding between clinicians and clients to what constitutes diversion. Motivations for diversion included "stockpiling" for later sublingual use (n = 15), discarding buprenorphine (n = 11), and giving it to another person (n = 5). A consistent definition of diversion of supervised dosed of buprenorphine is required. Diversion of supervised doses may represent a single episode of nonadherence to dosing instructions or more significant ambivalence over treatment. Responses to suspected diversion should aim to minimise harm and maximise treatment outcomes.