Type 1 17beta-hydroxysteroid dehydrogenase (17beta-HSD1) is a key steroidogenic enzyme that catalyses the reduction of steroid estrone into the most potent endogenous estrogen estradiol using the cofactor NAD(P)H. Bisubstrate inhibition is a good way to enhance the potency of inhibitors of cofactor-assisted enzymes. The design of a bisubstrate inhibitor of 17beta-HSD1, the estradiol/adenosine hybrid EM-1745, is reviewed and strategies for future designs of inhibitors are proposed.