Background: High levels of multidimensional perfectionism may be dysfunctional in their own right and can also impact on the maintenance and treatment of Axis I psychiatric disorders. Aims: This paper sought to describe the behavioural expressions and imagery associated with perfectionism in a non-clinical sample. Method: Participants (n = 59) completed a newly developed questionnaire to assess behavioural expressions of perfectionism, and an adapted interview to assess perfectionism-related intrusive mental images. Results: The study found that those high in perfectionism took longer to complete tasks, experienced more checking and safety behaviour whilst carrying out tasks, and had greater trouble actually completing tasks compared to those low in perfectionism. In addition, those with higher levels of perfectionism experienced intrusive mental imagery, which was more distressing, harder to dismiss, and had more impact on behaviour than those with lower levels of perfectionism. Conclusions: This research provides an initial exploration of the specific behaviours and intrusive mental imagery associated with perfectionism. The new behavioural measure of perfectionism could prove useful clinically in the assessment of change; however, these findings are preliminary and warrant replication in a clinical sample in order to examine their treatment implications.