OBJECTIVE: The purpose of this study was to evaluate the incidence of inability to flex proximal interphalangeal (PIP) and distal interphalangeal (DIP) joint in normal Koreans. The opposition palm ratio and thumb index ratio was also of interest. METHOD: Randomly selected eighty nine normal Korean adults of 48 men and 41 women, with ages 20 to 79 years. The finger flexion was measured using the standard flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP) screening tests. Thumb index ratio and opposition palm ratio was also assessed additionally. RESULTS: In the sample population, 2 subjects (2.2%) were unable to bilaterally flex their fifth PIP joints independently. Four subjects (4.4%) were unable to flex one or both of their fourth or fifth DIP joints. These results show far less incidence of FDS dysfunction comparing with 52% of FDS dysfunction rate in Americans. The opposition palm ratio in men were 63.6% and in women 69.9%, indicating lower ratio in men. The thumb index ratio was not different statistically between the men and women. CONCLUSION: These data suggest that the different incidences of FDS and FDP dysfunction should be considered in interpretation. The opposition palm ratio and thumb index ratio might be useful in the hand rehabilitation.