This paper presents quantitative and qualitative findings relating to the changes in surgical practice with the substitution of glyceryl trinitrate (GTN) ointment for surgery as a treatment for anal fissure. Activity and prescription data between 1994 and 1999, based on 650 cases treated at two large hospitals, showed significant changes over time in the volume and pattern of anal fissure surgery undertaken; this corresponded temporally with the growing availability of literature on non-surgical treatments for anal fissure. There was evidence of a progressive reduction in the number of surgeons undertaking this type of surgery and then a reduction in the volume of surgery undertaken by individual surgeons. Significant influences on practice over this period include the perceived importance of the innovation, which is in turn influenced by whether their predominant practice is coloproctology. Two models of decision making which result in adoption or non-adoption are presented. The data suggest that individual variation in the uptake of innovation, whether resistance to effective treatments or enthusiasm for ineffective ones, is neither random nor perverse. The findings suggest that an individual's basis for decision making, the degree to which the assessment of relative advantage is subjective or objective, and the process of trialling must all be considered as contributory factors.