Some 0.55 million people living in semi-urban and slum populations were screened for mental retardation by trained primary health centre (PHC) doctors, nurses and community health volunteers (CHVs). The staff were provided with prior training on the detection, prevention and diagnosis of mental retardation, prenatal diagnosis, and reproductive responsibilities. Field visits were employed to confirm diagnosed developmental disabilities, and demographic data incorporating social maps of 14 PHCs were prepared. Cases with high-risk genetic factors detected by PHC staff were referred to the Centre for Research in Mental Retardation (CREMERE) for cytogenetic and metabolic investigations, thus linking the study population and the Referral Centre. A genetic team interacted with the patient and family members for genetic counselling. Mental retardation was confirmed in 511 of the 525 cases reported, reflecting the positive impact of training on the CHVs. Potentially preventable environmental factors, such as birth asphyxia, infections, and low birth weight were identified in 251 cases (49%), 137 (27%) of which had additional genetic factors. Genetic causes were found in 186 (36%) individuals, the most common being Down syndrome. The study illustrates the urgent need for the integration of genetic screening into the public health services in India.