BACKGROUND: Tooth agenesis, the congenital absence of one or more teeth, can be diagnosed in children in the first decade of life. Tooth agenesis is a phenotypic feature of conditions such as ectodermal dysplasia, cleft lip, cleft palate, Down syndrome, and Van der Woude syndrome. Tooth agenesis can also be nonsyndromic. Studies have shown an association between the genetic determinants of nonsyndromic tooth agenesis and neoplasms in adulthood. METHODS: This review of the implications of tooth agenesis as a risk indicator for neoplasms in adulthood is based on a search of PubMed to identify published case series, case reports, and review articles. The reference articles were manually searched. The search was limited to articles published in the English language. RESULTS: Neoplasms reported in patients with tooth agenesis include colorectal neoplasms and epithelial ovarian cancer, as well as family histories of breast cancer, prostate cancer, and cancers of the brain and nervous system. CONCLUSION: Although odontogenesis and tumorigenesis may seem to be unrelated processes, the clinical association between the two highlights the overlap of genetic determinants and molecular pathways. Tooth agenesis can be diagnosed during childhood and should be considered a marker for risk of neoplasms in adulthood. Healthcare providers should identify tooth agenesis and provide appropriate anticipatory guidance.