Although it is often presumed that the molecular pathways that underlie normal organogenesis are similar to those perturbed during carcinogenesis, few examples exist of tissue-specific regulatory genes that play central roles in both processes. In the case of the prostate gland, molecular genetic analyses have demonstrated that the Nkx3.1 homeobox gene plays an important role in normal differentiation of the prostatic epithelium and that its loss of function is an initiating event in prostate carcinogenesis. Thus, the Nkx3.1 homeobox gene provides a paradigm for understanding the relationship between normal differentiation and cancer, as well as a model for studying the roles of homeobox genes in these processes. Here, we review recent findings concerning the biological as well as biochemical function of this central regulator of prostate development and carcinogenesis. Developmental Dynamics 228:767–778, 2003. © 2003 Wiley-Liss, Inc.