Aptitude tests are widely used in selection. However, despite certain advantages their use remains controversial. This paper aims to critically appraise five sources of evidence for the construct validity of the Health Professions Admission Test (HPAT)-Ireland, an aptitude test used for selecting undergraduate medical students. The objectives are to identify gaps in the evidence, draw comparisons with other aptitude tests and outline future research directions. Our appraisal of the literature found that stakeholder feedback indicates that there is reasonable evidence for test content validity for two of the three sections of HPAT-Ireland. By contrast the Non-Verbal Reasoning section is widely criticised as having limited relevance to medical school performance and future clinical practice. In terms of concurrent validity there is a significant small to medium, negative correlation with school exit examinations, but not consistently so across all studies (r = -0.18, -0.28, 0.017). Likewise predictive validity studies vary, from negative to moderate strength correlations with examination performance during early years at medical school. Five studies indicate that HPAT-Ireland is supported in principle by the majority of stakeholders. While one consequence of its introduction is that successful applicants are now coming from more diverse academic backgrounds, there is no evidence that the socio-economic background of medical school entrants has been altered significantly. Negative perceptions of unfairness relating to gender, coaching and socio-economics remain. The evidence to date suggests that while there are slight gender differences, initially favouring males, these vary year on year. In conclusion, the attitudes towards, and performance of, HPAT-Ireland is not unlike that of other aptitude tests widely used internationally. The main justifications for its introduction have been achieved, in that Ireland no longer relies exclusively on a single measure of academic record for selection to medical school. However a number of areas require further research and exploration.