The purpose of this study was to determine core nursing diagnoses (CNDs) from NANDA Taxonomy II for a cancer nursing information system supporting the nursing process. The main objective for determining CNDs was to increase the perceived usefulness and the perceived ease of use of the information system by supporting the process of making nursing diagnoses. The CNDs were for each of the patient groups of the six most common cancers in Korea. For the determination of CNDs, a survey and an analysis of patient records were performed. Two hundreds and nineteen clinical nurses participated in the survey and 72 patient records were analyzed. Based on the findings of the survey and analysis of patient records, 15 CNDs for each of the populations were determined.