We examined the frequency and kind of cancer in families with a child having a neoplasm at the Universitätskinderklinik Homburg/Saar, at the Universitätskinderklinik Freiburg and at the Institut für Medizinische Statistik und Dokumentation der Johannes Gutenberg-Universität Mainz. The following could be shown: 1. There is no difference in the distribution of various kinds of cancer in children, whether they have relatives with cancer or not. 2. It is necessary to examine the family history repeatedly to obtain an accurate documentation of familial cancer. 3. Cancer in familial members did occur in a third of all families on an average. 4. Independently of the diagnosis of the child, in most families only one additional family member did have cancer. 5. The majority of relatives with cancer are grandparents. 6. Cancer of the lung and of the breast are the most frequent kinds of neoplasms occurring in family members. 7. Comparing the most frequent kinds of neoplasms in family members in this study with the distribution of cancer in adults, it is obviously, that there is a higher percentage of leukemia and brain tumors in relatives of children with cancer than is expected. 8. Typical tumor constellations can be found in affected families like breast cancer and soft tissue sarcomas.