Although inherited p53 mutations are present in all somatic cells, malignant transformation is limited to certain organs and target cells. The analysis of 475 tumors in 91 families with p53 germline mutations reported since 1990 shows that breast carcinomas are most frequent (24.0%), followed by bone sarcomas (12.6%), brain tumors (12.0%), and soft tissue sarcomas (11.6%). The sporadic counterparts of these tumors also carry a high incidence of p53 mutations, suggesting that in these tissues p53 mutations are capable of initiating the process of malignant transformation. Hematological neoplasms (acute lymphoblastic leukemia and Hodgkin's lymphoma) and adrenocortical carcinomas occurred at a frequency of 4.2 and 3.6%, respectively. One-half of the families fulfilled the diagnostic criteria of the Li-Fraumeni syndrome. There were marked organ-specific differences in the mean age at which carriers of p53 germline mutations present with neoplastic disease: 5 years for adrenocortical carcinomas, 16 years for sarcomas, 25 years for brain tumors, 37 years for breast cancer, and almost 50 years for lung cancer. Analysis of the mutational spectrum showed a predominance of G:C-->A:T transitions at CpG sites, suggesting an endogenous formation, eg, by deamination of 5-methylcytosine, rather than a causation by environmental mutagenic carcinogens. The location of mutations within the p53 gene was found to be similar to that of somatic mutations in sporadic tumors. There is no evidence of an organ or target cell specificity of p53 germline mutations; the occasional familial clustering of certain tumor types is more likely to reflect the genetic background of the respective kindred or the additional influence of environmental and nongenetic host factors.