The results of study on 2009 people who use high arsenic contaminated groundwater in 5 provinces and cities including Hanoi, Ha Nam and Hung Yen, Dong Thap and Tien Giang showed that: the rate of people in the studied sites with content of arsenic in the hair is 27.2 percent compare to permitted level, in which, 15.9 percent of the people with content of arsenic is over 0.8 mg/kg of hair. The average of arsenic content in the hair tended to increase with age. The average of arsenic content in hair is the highest in age group of over 60 years old (0.60 + or - 0.03 mg/kg of hair), while in other groups ranged from 0.41 to 0.50 mg/ kg of hair. The rate of people with test results of arsenic content in hair was the highest in age group of over 60 years old (27.8 percent), and the lowest in age group of under 6 years old (9.6 percent). The average of arsenic content in hair in of men is higher than in hair of women (men: 0.60 + or - 0.03 mg / kg, women: 0.46 + or - 0.02 mg/kg).