The relationship between malnutrition and intellectual performance was studied in 1336 rural primary school children (6-8 yr). Observations showed that the relative risk of having an IQ less than or equal to 89 in severe, moderate and mild malnutrition was 3.5, 2.7 and 1.4 times for boys and in girls it was 2.4, 1.7 and 1.4 times respectively. Mean full scale, verbal and performance IQ as well as the scores for various subtests decreased with the severity of malnutrition. However, though the decrease in IQ scores was significant, below average performance of malnourished children was observed only for performance IQ (87.6 +/- 9.13), and subtests information (87.9 +/- 10.5), digit span (79.6 +/- 11.9), picture completion (88.6 +/- 13.9), object assembly (81.1 +/- 18.1), and coding (80.5 +/- 14.4). Further, the stunted children had lower IQ scores as compared to those who were wasted. Multiple regression analysis showed that besides nutrition, socio-economic status had significant influence on verbal IQ; economic sufficiency on picture completion and block design, psychosocial and family environment on vocabulary and digit span subtests. However, the values of correlations obtained were too low to be used for prediction of scores. The overall observations demonstrate that even moderate degree of malnutrition influences the IQ scores and its effect is of a higher magnitude on immediate memory, visual perception, and visual motor integration as compared to verbal reasoning and comprehension.