Carcinogenesis of hormone-related cancers involves hormone-stimulated cell proliferation, which increases the number of cell divisions and the opportunity for random genetic errors. In target tissues, steroid hormones are interconverted between their potent, high affinity forms for their respective receptors and their inactive, low affinity forms. One group of enzymes responsible for these interconversions are the hydroxysteroid dehydrogenases, which regulate ligand access to steroid receptors and thus act at a pre-receptor level. As part of this group, the 17β-hydroxysteroid dehydrogenases catalyze either oxidation of hydroxyl groups or reduction of keto groups at steroid position C17. The thoroughly characterized 17β-hydroxysteroid dehydrogenase type 1 activates the less active estrone to estradiol, a potent ligand for estrogen receptors. This isoform is expressed in gonads, where it affects circulating levels of estradiol, and in peripheral tissue, where it regulates ligand occupancy of estrogen receptors. Inhibitors of 17β-hydroxysteroid dehydrogenase type 1 are thus highly interesting potential therapeutic agents for the control of estrogen-dependent diseases such as endometriosis, as well as breast and ovarian cancers. Here, we present the review on the recent development of inhibitors of 17β-hydroxysteroid dehydrogenase type 1 published and patented since the previous review of 17β-hydroxysteroid dehydrogenase inhibitors of Poirier (Curr. Med. Chem., 2003, 10, 453). These inhibitors are divided into two separate groups according to their chemical structures: steroidal and non-steroidal 17β- hydroxysteroid dehydrogenase type 1 inhibitors. Their estrogenic/ proliferative activities and selectivities over other 17β-hydroxysteroid dehydrogenases that are involved in local regulation of estrogen action (types 2, 7 and 12) are also presented.