Ability patterns and surgical proficiency were examined in matched groups of general surgery residents selected on the basis of age, gender, or hand preference from a population of 141 residents who had completed neuropsychologic tests of visuospatial, psychomotor, and stress tolerance abilities and had been rated on 12 aspects of technical skill exhibited during 1480 operative procedures. Older residents (ages 28 to 42 years) exhibited less motor speed (p less than 0.05) and coordination (p less than 0.005) and more caution in avoiding psychomotor errors (p less than 0.05) than did their younger counterparts. No differences were found for visuospatial abilities, stress tolerance, or rated surgical skill. These findings indicate that although age does appear to adversely affect pure motor skills, these are not important components of operative proficiency. Female residents exhibited superior (p less than 0.05) academic achievement (MCAT, Verbal and National Boards Part II) as compared with their male counterparts. They also excelled on a signal detection task requiring identification of visual patterns. However, the women scored less well (p less than 0.05) than men on a visuomotor task demonstrated to be a significant predictor of operative skill. Greater cautiousness in avoiding errors may be a contributing factor to their reduced efficiency on this task. In comparison to male controls, female residents received consistently lower surgical skills ratings, particularly on items measuring confidence and task organization. Left-handed residents were more reactive to stress (p less than 0.03), more cautious (p less than 0.04), and more proficient on a neuropsychologic test of tactile-spatial abilities (p less than 0.03) than right-handed counterparts. Although these traits correlated positively (p less than 0.05) with rated operative skill within the left-handed group, the group received consistently lower ratings than did right-handed residents. The inconvenience of assisting left-handed residents may overshadow attending surgeons' perceptions of their innate abilities. These findings demonstrate significant, neuropsychologically based differences among surgery residents that pose unique challenges to persons responsible for their selection and training.