Objective: Sudden, unwelcome and repetitive thoughts about a traumatic event – intrusive thoughts – could relate to how men assess their quality of life after prostate cancer diagnosis. We aimed to study the prevalence of intrusive thoughts about prostate cancer and their association with quality-of-life outcomes before and after surgery.

Method: During the first year of the LAPPRO-trial, 971 men planned for radical prostatectomy were prospectively registered at 13 urological centers in Sweden. Of those, 833 men responded to two consecutive study-specific questionnaires before and three months after surgery (participation rate 86%).

Results: Before surgery, 603 men (73%) reported negative intrusive thoughts about their cancer at some time in the past month and 593 men (59%) reported such thoughts three months later. Comparing those reporting intrusive thoughts at least weakly before surgery with those who did not, the prevalence ratio (95% confidence interval) three months after surgery for waking up in the middle of the night with anxiety was 3.9 (2.7 to 5.5), for depressed mood 1.8 (1.6 to 2.1) and for impaired self-assessed quality of life 1.3 (1.2 to 1.5).

Conclusions: The prevalence of negative intrusive thoughts about prostate cancer at the time of surgery associates with impaired quality of life three months later. It could be valuable to design clinical interventions that diminish the occurrence of negative intrusive thoughts in men with prostate cancer diagnosis.