A statewide cross-sectional survey was conducted in Australia to identify the determinants of registered nurses' intention to administer opioids to patients with pain. Attitudes, subjective norms and perceived control, the key determinants of the Theory of Planned Behavior, were found to independently predict nurses' intention to administer opioids to these patients. Perceived control was the strongest predictor. Nurses reported positive overall attitudes towards opioids and their use in pain management. However, many negative attitudes were identified; for example, administering the least amount of opioid and encouraging patients to have non-opioids rather than opioids for pain relief. The findings related to specific attitudes and normative pressures provide insight into registered nurses' management of pain for hospitalized patients and the direction for educational interventions to improve registered nurses' administration of opioids for pain management.