Since 1998 the Synthetic Personality Inventory (SPI), a well-established aptitude test, has been used to select residents at St. Luke's International Hospital. The aims of our study were to analyze the association of the SPI with several characteristics of residents, e. g., intellectual capability, results of examinations in medicine, and evaluation during 2 years of residency, and to clarify the significance of the SPI for selecting residents. General mental ability measured with the SPI was strongly correlated with the intellectual capability of residents but was not correlated with results of examinations in medicine. High scores for general mental ability, for activity, and for tendency of extroversion were correlated with high evaluations of residents for 2 years, whereas a cooperative personality, reasoning ability, and practicality were related to an improvement in grades from the first to second years. These results demonstrate that the results of the SPI are correlated with several characteristics of residents.