The Morphometric Analysis of the Brachial Plexus Formation in Human Fetuses. This study was carried out in 100 fetuses (75; 2nd trimester, 25; 3rd trimester) and totally 200 brachial plexus were evaluated under examination stereomlcroscope. After bilateral fine dissection, to perform morphometric stu- dies; the thickness and/or length of the each part that contribute to the formation of the brachial plexus were me- asured by calipers. Photographs of the brachial plexuses were taken after dissection. Data was statistically analy- sed by Pearson correlation and Student t-tests using SPSS softvvare (for vvindovvs 8.0). İn this study, 93 fetuses vvere decided as normal (the brachial plexus consist of the 5th, 6th, 7th, 8th cervical nerves and 1st thoracic nerve). The mean value of the length of the 8th cervical, 1st thoracic, upper trunk and middle trunk showed sta­ tistically significant difference betvveen female and male. The mean value of the thickness of the posterior di­ vision of lower trunk showed statistically significant difference betvveen right and left side. There was no sig­ nificant difference in other parameters. Pegarding to the correlation values betvveen the age and the measured parameters, the grovvth rate of the each part that contribute to the formation of the brachial plexus was higher in 2nd trimester than in 3rd trimester. The reported results may provide useful information about the fetal de- velopment of peripheral nervous system, and in the diagnostic and therapeutic approach of paediatric surgeons for preventing complications.