Despite the fact that as many as 80-90% of patients with cancer pain can be effectively treated using pharmacological therapies and other advanced approaches, 31% to 85% of cancer patients in Taiwan still experience varying levels of pain. Pain is one of the symptoms that patients fear most; it overwhelms all aspects of patients' lives and creates a sense of uncertainly and hopelessness. Pain control is, therefore, a high priority in the treatment of cancer patients. Pharmacological therapy is the cornerstone of cancer pain management. With the current trend toward outpatient care, many patients are being required to assume greater responsibility for self-management of prescribed analgesics at home to deal with the variable and complex nature of cancer pain and side effects of opioids. Patients however, have misconceptions regarding analgesics and a series of difficulties when attempting to put a pain management regimen into practice. This research addressed the hypothesis that self-efficacy beliefs might play an important role in analgesic adherence and pain experience in Taiwanese outpatients with cancer. The purpose of this study was to develop a scale to measure the self-efficacy expectations relating to opioid-taking in Taiwanese outpatients with cancer. Another purpose was to explore how opioid-taking self-efficacy and beliefs about opioid analgesics contribute to patients' analgesic adherence and pain experience in Taiwanese outpatients with cancer. In the first stage semi-structured interviews were conducted to collect data from a purposeful sample (n=10) of oncology outpatients from two teaching hospitals in the Taipei area of Taiwan. The purpose of this phase was to identify behaviours and situational impediments associated with analgesic taking. Findings from this phase were used to develop a scale to measure opioid-taking self-efficacy. In the second stage a pilot test with a convenience sample (n=30) was conducted to test the validity and reliability of the new scale and to identify the feasibility of using the scale in a cross-sectional survey. In the third stage a cross-sectional survey was undertaken (n=92) to describe pain experiences, analgesic adherence, beliefs about opioid analgesics, and opioid-taking self-efficacy in Taiwanese outpatients with cancer and to explore how opioid-taking self-efficacy and beliefs about opioid analgesics contributed to analgesic adherence and pain experience. Results of this study highlight an important issue - under-treatment of cancer pain in this group of Taiwanese outpatients. As well, low adherence rates to opioid analgesics in cancer outpatients arose as an important issue in this study. A range of misconceptions about using opioids for pain was also common amongst the sample. Despite these misconceptions, patients reported being moderately confident in their ability to perform self-management behaviours related to their prescribed opioid-taking. Results of this research supported the notion that patients' self-efficacy in relation to taking their prescribed opioid regimen was a significant independent predictor of patients' adherence behaviour and pain relief, but not of pain severity. Beliefs about opioid analgesics were also an independent predictor of patients' adherence, but not of pain relief or pain severity. In addition, findings from this study provided support for the validity and reliability of the opioid-taking self-efficacy scale. Results suggested there is a need for systematic assessment of beliefs affecting patients' opioid adherence behaviours for cancer pain control, including perceived personal self-efficacy and beliefs about opioid analgesics. Educational programs that focus on overcoming patients' misconceptions (beliefs) about taking opioid analgesics may be particularly beneficial. In addition, this study advocates that conducting self-efficacy-enhancing interventions may improve medication adherence for patients and therefore pain relief. More research is needed to demonstrate the construct validity of the self-efficacy scale and to evaluate self-efficacy enhancing interventions in cancer pain management.