Background: Online evidence retrieval systems are a potential tool in supporting evidence-based practice. Effective and tested techniques for assessing the impact of these systems on care delivery and patient outcomes are limited. Purpose and methods: In this study we applied the critical incident (CI) and journey mapping (JM) techniques to assess the integration of an online evidence system into everyday clinical practice and its impact on decision making and patient care. To elicit incidents semi-structured interviews were conducted with 29 clinicians (13 hospital physician specialists, 16 clinical nurse consultants (CNCs)) who were experienced users of the online evidence system. Clinicians were also asked questions about how they had first used the system and how their use and experiences had changed over time. These narrative accounts were then mapped and scored using the journey mapping technique. Results: Clinicians generated 85 critical incidents. Three categories of impact were identified: impact on clinical practice, impact on individual clinicians and impact on colleagues through the dissemination of information gained from the online evidence system. One quarter of these included specific examples of system use leading to improvements in patient care. Clinicians obtained an average journey mapping score of 22 out of a possible score of 36, demonstrating a good level of system integration. Average scores of doctors and CNCs were similar. However individuals with the same scores often had very different journeys in system integration. Conclusions: The CI technique provided clear examples of the way in which system use had influenced practice and care delivery. The JM technique was found to be a useful method for providing a quantification of the different ways and extent to which, clinicians had integrated system use into practice, and insights into how system use can influence organisational culture. The development of the journey mapping stages provides a structure by which the program logic of a clinical information system and its desired outcomes can be made explicit and be based upon users' experiences in everyday practice. Further work is required using this technique to assess its value as an evaluation method.