There are no published instruments of patient self-efficacy related to medication behaviour, yet understanding and promoting medication compliance are central to nursing practice. The purpose of this qualitative study was to explore patient perceptions, experiences and practices associated with long-term medication behaviour in order to establish an instrument measuring self-efficacy in medication behaviour. In-depth interviews were conducted with 14 patients with lifelong dependency on medicine. Using a phenomenological method of analysis the following themes emerged, all of which could be integrated within Bandura's conceptualization of dimensions of self-efficacy. The dimension of personal attributes comprised the themes of emotional distress, confidence in the physician, perceived health status, and normalcy. Environmental factors included the themes of routine, distraction, social support and cost of medication. The third dimension of self-efficacy, task-related and behavioural factors was composed of the themes of side-effects, drug delivery system, medication aids, medication schedule, and knowledge. Based on these themes, items for the Long-Term Medication Behaviour Self-Efficacy Scale, were developed and integrated into a version that is currently being submitted to further psychometric work.