OBJECTIVE: To determine how primary health care physicians differ in their ability and the factors underlying the differences between them in the ability to recognize mental disorders. METHOD: The group studied consisted of 15 primary health care physicians detecting mental disorders in 750 randomly selected adult patients of the general practice clinic in Thammasat University Hospital. The GHQ-28-Thai version was used as the reference method in the identification of psychiatric cases compared with the physicians' own assessment. Univariate and multivariate statistical analysis were used. RESULTS: There was a great variation in the ability of the physicians to detect mental disorders. The recognition ability was associated with the medical school from which the physician graduated. The discrimination ability was not associated with any factors. CONCLUSION: The medical school plays a role in determining the ability to detect mental disorders. This information would usually inform future developments in psychiatry teaching at both undergraduate and postgraduate levels.