Background: The number of cancer survivors, including childhood cancer survivors, is increasing as a consequence of improved therapeutic options. However, the medical costs associated with therapy are high and many families are suffering from the resultant financial burden. Objective: Our study aims to determine the total medical cost for 5 years after the initial diagnosis of childhood cancers. Methods: A customized dataset from the Korean National Health Insurance Claims Database was requested for this study. A total of 7,317 patients were selected to determine the total medical cost related to their treatment. The costs are presented as the 2% trimmed mean value to exclude extreme costs. The medical costs were further classified according to cancer type, treatment phase, and socioeconomic status. Multiple linear regression analyses were performed. Results: The average total medical cost per patient is 36.8 million Korean Wons (KRW) or 30,665 United States Dollars (USD). Among childhood cancers, leukemia was associated with the highest cost at 53.5 million KRW (USD 44,556). Analysis of socioeconomic status revealed that the higher income group demonstrated higher medical expenditure when compared to other groups. Analysis of the treatment phase showed that costs associated with the early phase of treatment are the highest, especially in the first 3 months after initial diagnosis. Conclusion: Cancer treatments are expensive and are a source of significant financial stress to patients’ families. To alleviate the financial burden and reduce the socioeconomic disparities associated with medical care and costs, a better understanding of the current experience of patients and their families is required.