Contamination of groundwater by arsenic, a paradoxical human carcinogen, has become a cause of global public health concern. In West Bengal, India, the groundwater in 9 of 18 districts is heavily contaminated with arsenic. Various adverse health effects including cancer have been reported from these districts and are associated with prolonged arsenic exposure. A cross-sectional biomarker study was conducted to evaluate and compare the frequencies of micronuclei in peripheral blood lymphocytes, oral mucosa cells, and urothelial cells from the inhabitants of North 24 Parganas, one of the arsenic-affected districts. The three cell types were collected from 163 residents exposed to high levels of arsenic in drinking water (214.7213 +/- 9.0273 microg/l) and from 154 unexposed subjects residing in the unaffected East Midnapur district with very little or no exposure to arsenic through drinking water (9.2017 +/- 0.3157 microg/l). Our analysis revealed that micronuclei frequencies in the exposed group were significantly elevated to 5.33-fold over unexposed levels for lymphocytes, 4.63-fold for oral mucosa cells, and 4.71-fold for urothelial cells (increases in micronuclei frequencies significant at P < 0.01). The results indicate that chronic ingestion of arsenic in drinking water by the exposed subjects is linked to the enhanced incidence of micronuclei in all the three cell types, slightly higher level of micronuclei being observed in lymphocytes compared with oral mucosa and urothelial cells.