Groundwater contamination by arsenic is a serious environmental problem in the world. Yet there have been few studies conducted in Southeast Asian countries. This article surveys arsenic contamination in groundwater and residents from Vietnam, and is based on our previous studies. Samples of groundwater (n = 118), human hair (n = 59), and urine (n = 100) were collected in the Red River and Mekong River Deltas during 2001-2004. Arsenic was detected in most of the groundwater samples, and its level ranged from &lt
0.1 to 486 μg/l. Elevated concentrations of arsenic were observed in groundwater at some locations in Ha Nam (up to 486 μg/l) in the Red River Delta and Dong Thap (up to 411 μg/l) in the Mekong River Delta. Remarkably, about 33% of these groundwater samples exceeded the WHO drinking water guideline of 10 μg/l. These results suggest that arsenic contamination in groundwater may be widely present in both the Red River and Mekong River Deltas, Vietnam. A significant positive correlation was observed between arsenic concentrations in groundwater and human hair. Arsenic speciation of human urine revealed the presence of inorganic arsenic, and these concentrations positively correlated with arsenic levels in groundwater. Thus, it is likely that residents in our study areas are chronically exposed to arsenic through drinking groundwater, suggesting that there is a health risk from arsenic in Vietnam.