The National Nutrition Survey estimates the average dietary intake per capita by household-based food consumption data. The dietitians at local public health centers manually execute coding of food names, the amount totally consumed and the proportion shared by family members to compute nutrient intake of individual subjects. The coded data are then checked and corrected by other dietitians at prefecture departments. We examined error sources in both procedures, and described the frequency of errors and their effect on calculation of energy and nutrients intakes by using a sub-sample, 132 households including 445 family members, of the 1995 survey. The errors on coding the foods and the totally consumed amount, including no-coding for a specified food occurred at 1.61 per household, and those on coding the proportion shared by family members at 0.19 on the level of public health centers, respectively. Those frequencies at prefecture departments were 1.57 and 0.16 per household, respectively. This suggested tht satisfactory. In conclusion, we recommend that a new system for coding and data entry by use of personal computer software should be provided to public health centers. The system will have automatic error checking procedures by incorporating a food code list and upper limits for the acceptable values for each food.