Background: Textbooks are a formative resource for health care providers during their education and are also an enduring reference for pathophysiology and treatment. Unlike the primary literature and clinical guidelines, biomedical textbook authors do not typically disclose potential financial conflicts of interest (pCoIs). The objective of this study was to evaluate whether the authors of textbooks used in the training of physicians, pharmacists, and dentists had appreciable undisclosed pCoIs in the form of patents or compensation received from pharmaceutical or biotechnology companies. Methods: The most recent editions of six medical textbooks, Harrison’s Principles of Internal Medicine (HarPIM), Katzung and Trevor’s Basic and Clinical Pharmacology (KatBCP), the American Osteopathic Association’s Foundations of Osteopathic Medicine (AOAFOM), Remington: The Science and Practice of Pharmacy(RemSPP), Koda-Kimble and Young’s Applied Therapeutics (KKYAT), and Yagiela’s Pharmacology and Therapeutics for Dentistry (YagPTD), were selected after consulting biomedical educators for evaluation. Author names (N = 1,152, 29.2% female) were submitted to databases to examine patents (Google Scholar) and compensation (ProPublica’s Dollars for Docs [PDD]). Results: Authors were listed as inventors on 677 patents (maximum/author = 23), with three-quarters (74.9%) to HarPIM authors. Females were significantly underrepresented among patent holders. The PDD 2009–2013 database revealed receipt of US$13.2 million, the majority to (83.9%) to HarPIM. The maximum compensation per author was $869,413. The PDD 2014 database identified receipt of $6.8 million, with 50.4% of eligible authors receiving compensation. The maximum compensation received by a single author was $560,021. Cardiovascular authors were most likely to have a PDD entry and neurologic disorders authors were least likely. Conclusion: An appreciable subset of biomedical authors have patents and have received remuneration from medical product companies and this information is not disclosed to readers. These findings indicate that full transparency of financial pCoI should become a standard practice among the authors of biomedical educational materials.