To determine clinical aptitude (AC) in occupational medicine residents. An instrument based on real clinical cases was built and validated to assess AC, which was composed by surveillance indicators of the workers health (SIWH) and occupational-medical evaluation indicators (0ME) In the study participated 22 undergraduate students (UE), 40 residents of first year (R1) and 36 of second year (R2). The instrument was validated by experts. Internal consistency of the instrument was 0.93 by Kuder-Richardson. Regarding global AC, 96 % of UE were situated in a random level and 4 % in a very low level. 15 % of R1 was situated in a random level, 50 % in a very low level, 30 % low level and 5 % in medium level; whereas R2 3 % was positioned in a random level, 28 % in a very low level, 50 % in low level and 19 % in medium level. A significant difference was found between R1 and R2 in occupational-medical evaluation (p < 0.009), but not in SIWH. Two centers showed statistical difference in both indicators.