Background: Mental contamination is a psychological sense of contamination that involves an internal, emotional feeling of dirtiness that may be evoked by unwanted thoughts and images, such as sexual assaults. Aims: This study aimed to investigate which types of unwanted sexual experiences evoke the strongest mental contamination, and to test the hypothesis that cognitive appraisals of an unwanted sexual experience predict indices of mental contamination (i.e. feeling of dirtiness, urge to wash, internal negative emotions, and external negative emotions). Method: 148 female participants were asked to recall their most distressing unwanted sexual experiences. Indices of mental contamination and cognitive appraisals of the experience were then assessed. Results: Our findings indicated that individuals recalling experiences related to rape felt more intense feelings of dirtiness than individuals recalling other types of unwanted sexual experience, such as verbal sexual assault, visual sexual assault, and forcible touching/frottage. In addition, hierarchical regression analyses demonstrated that a cognitive appraisal of perceived violation predicted all of the indices of mental contamination after controlling anxiety, depression, and fear of contact contamination. Conclusions: The present study demonstrated that an individual is at greatest risk of mental contamination if she has experienced rape/attempted rape, and if she makes a cognitive appraisal of violation regarding the incident.