Trainee psychologists, like those completing a postgraduate master's programmes are vulnerable to experiencing impostorism. To help assess this risk and develop intervention strategies, there is a need for a brief validated measure of impostorism. The Leary Impostorism Scale (LIS) is a brief self-report measure that demonstrates satisfactory psychometric properties but has not been validated with trainees undertaking professional psychology training. The current study involves an exploratory factor analysis (EFA) of the LIS and describes levels of impostorism in a sample of Australian trainee psychologists. Participants were 161 postgraduate students enrolled in their first year of a psychology master's programme. A maximum likelihood (ML) EFA revealed a single factor accounted for 73.67% of total variance. Parallel analysis verified the unidimensional model. A Cronbach's [alpha] of 0.94, was obtained indicating high internal consistency. Overall, the sample scored at 'moderate' levels with 23% having high levels of impostorism. Further research is required to investigate further item reduction of the LIS due to high internal consistency. In addition, to clarifying factors that may account for differences between levels of impostorism between participants in different training programmes, there is a need to develop and assess interventions to reduce the negative effects of impostorism.