Aim. This paper is a report of a study to describe nurses' perceptions of decision-making and the evidence base for the initiation of insulin therapy.Background. Several theoretical perspectives and professional's attributes underpin decision-making to commence insulin therapy. The management of type 2 diabetes is moving from secondary to primary care and this affects how clinical decisions are made, by whom and the evidence base for these decisions.Method. A postal survey was conducted with a stratified sample of 3478 Diabetes Specialist Nurses and Practice Nurses with a special interest in diabetes across the four countries of the United Kingdom. A total of 1310 valid responses were returned, giving a response rate of 37·7%. The questionnaire was designed for the study and pilot-tested before use. Responses were given using Likert-type scales. Data were collected during 2005 and 2006, and one reminder was sent.Results. People with diabetes are seen as having little influence in decision-making. Consultant physicians appear to be influential in most decisions, and the nursing groups held varying perceptions of who made clinical decisions. Nurses' identified different responsibilities for those working solely in secondary care from those working in both community and secondary care. Practice nurses were not as involved as anticipated.Conclusion. Nurses working with people with diabetes need to encourage them to become more active partners in care. Clinical guidelines can assist in decision-making where nurses are least experienced in initiating insulin therapy.