An experimental study of the design and implementation of a special preparatory booklet designed to reduce stress in surgical patients is reported. Patients in this study were 63 women undergoing minor gynaecological surgery. They were allocated sequentially to three groups: routine care only (control group), routine care plus a minimally informative booklet (placebo group) and routine care plus a maximally informative booklet (experimental group). Changes in cognitive variables were assessed prospectively over the course of hospitalization and surgery. As expected, the intervention had direct effects on patients' knowledge, reported information and worries about surgery. It also had indirect beneficial effects on the amount of reported information and support from staff and families. Finally, patients in the placebo group were found to have more misconceptions about surgery and to more often report anxiety in communication with staff and in association with reading materials. Partial correlation analyses showed that patients who have more knowledge about surgery have fewer worries and recover faster. The implications for cognitive theories of the process of stress reduction for surgical patients by psychological preparation are discussed.