History and Objectives: An appropriate mental function is required for optimum performance in every age. There are evidences on the relationship between intestinal infection and effective mental performance. This study was carried out to determine the incidence of infection due to intestinal parasites and its relationship with mental performance in students of Robat Karim region from 1998 to 1999.

Materials and Methods: The descriptive strategy of this study was conducted on 268 girls and 332 boys with an age range of 6-12 years. For sampling, cluster method was applied on 128 schools in the region. After examination of feces using direct and ether methods, 150 contaminated children were chosen as case group and 150 healthy children were selected as control. Both groups were similar regarding sociological, economical, cultural and nutritional status. For evaluation of mental performance, coding, arithmetic, digit-span forward/backward and fluency tests were used.

Results: The incidence rate of contamination was 28.7% and arithmetic marks of control, cases with protozoal and/or helminthic infection was 8.44±2.59, 7.9±2.73 and 7.67±2.45 respectively. In addition, the groups were similar regarding coding, but fluence was 4.61±2.46, 4.79±2.59 and 4.33±2.5 respectively (P<0.03). Mental performance was 7.82±2.78 and 6.5±2.92 respectively (P<0.004). The most common form of parasites among children was Giardia lamblia.

Conclusion and Recommendations: It is concluded that healthy students have a higher mental performance and it is recommended to treat cases with parasitic contamination.