Background & Aims: The nonapproved use of human growth hormone (HGH) for anti-aging has been increasing. Theoretical concerns for neoplastic potentiation by HGH have been raised, but not proven clinically. Methods: We report the case of a 68-year-old man with colonic Crohn's disease who was found to have aggressive metastatic colon cancer. The patient had been receiving HGH therapy for anti-aging purposes for 7 years before presentation. Normal and malignant colonic tissue was examined for qualitative and quantitative molecular profiles of growth hormone (GH) and its signaling molecules, using immunohistochemistry and RNA extraction with polymerase chain reaction amplification. Results: Immunoreactivity was more robust in tumor tissue than in normal colon for insulin-like growth factor-1 receptor (IGF-1R) but not for IGF, GH, or GH receptor. RNA extraction with quantitative polymerase chain reaction showed that IGF-1R and vascular endothelial growth factor expression, but not IGF-1, GH receptor, or suppressor of cytokine signaling-2, were higher in tumor than in normal colonic tissue. Conclusions: Colorectal cancer development concurrent with administration of HGH for anti-aging purposes occurred in an individual already at increased risk for colon cancer. This underscores the need for further investigation of the proneoplastic potential of GH supplementation for anti-aging. © 2008 AGA Institute.