This paper describes a study that aimed to identify the extent to which feigning of mental illness represents a significant problem in prisoners referred to a medium secure unit. A clinical method was used to assess the prisoners, employing the Structured Interview of Reported Symptoms (SIRS) and selected Minnesota Multiphasic Personality Inventory-2 (MMPI-2) validity indices. Stringent criteria were used to classify 60 consecutive referrals to a secure unit as feigning mental disorder or not. In addition, the study examined characteristic differences, on a number of selected variables, between those prisoners who feign and those who respond honestly. The personality profiles of prisoners who feign were also investigated. Analysis of data showed that 32% of the sample (P < 0.01) could be classified as fabricating or exaggerating symptoms of mental illness. It is suggested that such presentations may be more prevalent than previously considered. Few differences were observed between the groups on selected variables, although prisoners who feigned mental illness demonstrated significantly higher dependent and anxious (avoidant) personality types. The implications of the findings are discussed in relation to available models of feigned presentations.