Objective:At the beginning of present study, the aim was to determine the differences of intelligence and management of the dominant hemispheres and anatomical asymmetry in monozygotic (MZ) twin pairs (Erkec and Yetkin, 2009). Between their asymmetric functions, unexpectedly some monozygotic twins were found discordant for handedness. Methods: To assess the hand preferences, Edinburgh Handedness Inventory (EHI) and Yetkin Laterality Questionnaire (YLQ) were used. In addition Cattle Culture Free Intelligence Test (CCFIT) was used to determine the intelligence (IQ). Adler's Brain test was also used to assess the hemispheric management. Results: In handedness, 27 discordant twins were found by using EHI and YLQ, respectively. The average of hand preference between twin pairs was -31.29 % and 65 %, but according to YLQ the value was found - 11.12 %, 57.25 According to EHI, among 15 MZ twin, a pair was found left- and right handed, a MZ twin pair was including one left handed and other mixed hand, in 11 MZ twins pairs one of them was right- and other one was ambidexterity. According to YLQ, in 11 MZ twin pair one of the twins was right- and other one was left handed, and in 20 MZ twin pairs one of twin was right hander and other one was ambidexterity. IQ degree was determined in 3 MZ twin pairs discordant for handedness age up to thirteen. Dominant hemisphere management was 4.82 % in average. Conclusions: The study on the twins is important either biological and physiological process or environmental affects. In MZ twins it is expected that they can use their hands in similar way, left hand or right hand. In contrast, in this study is shown that some twins can use their hand in different preferences. This study is a part of the project in number of HSI -2006-099 supported by YYU-SRPD, Van, Turkey.