Immunization is one of the major public health interventions to prevent childhood morbidity and death. Without immunization, more than five million children would die every year due to vaccine preventable diseases. Immunization will become more effective if the children receive the full course of recommended immunization doses. However, due to various circumstances, many fail to complete the course of immunization. In North Sumatra province, the immunization coverage in 1997 was the lowest in Indonesia, of which only 36 per cent of children (12-23 months) were fully immunized. The objective of this study was to examine the factors affecting the status of childhood immunization in North Sumatra province, Indonesia. In this study, secondary data from the Indonesia Demographic and Health Survey 1997 was used. The subjects considered in this study were 599 children aged 12-59 months. To study the factors affecting the status of childhood immunization, thirteen variables under four broad categories, namely, characteristics of mothers, characteristics of fathers, characteristics of children, and characteristics of households were selected. The findings showed that 41 per cent of the children received complete immunization. Among thirteen variables, which were considered to influence immunization status of children, nine variables were found to have statistically significant relationship with the completeness of immunization. They are maternal education, maternal occupation, prenatal care, father's education, father's occupation, birth order, place of delivery, assistant at delivery, and household's economic status. There is no relationship between immunization status and maternal age, age of child, sex of child, and place of residence. It is therefore recommended that programs need to focus on special health education programs for parents, particularly at the low socioeconomic level. Mothers also need to be given special education to encourage them to immunize their children and also to raise their awareness regarding the necessity for complete immunization.