Studies evaluating decisions aids have used a wide range of outcome measures as well as formats and settings. Most studies have focused on patient decision aids used either within the consultation or delivered pre-consultation, but there are no randomised, controlled studies comparing the two. However, timing and format of the patient decision aid intervention may affect how useful the tool is to the patient. The aim of this project is therefore to deepen our understanding of the patient's engagement in and preparation for the decision making process in a randomised, controlled trial comparing an electronic pre-consultation and paper-based in-consultation patient decision aid. 274 patients with colorectal and breast cancer are enrolled in the study. Data are collected at both patient and consultant perceived levels as well as an observed level of shared decision making.