Lysine specific demethylase 1 (LSD1) plays an important role in regulating histone lysine methylation at residues K4 and K9 on histone H3 and is an attractive therapeutic target in multiple malignancies. Here we report a structure-based virtual screen of a compound library containing ~2 million small molecular entities. Computational docking and scoring followed by biochemical screening, led to the identification of a novel N'-(1-phenylethylidene)-benzohydrazide series of LSD1 inhibitors with hits showing biochemical IC50s in the 200-400 nM range. Hit-to-lead optimization and structure-activity relationship studies aided in the discovery of compound 12, with a Ki of 31 nM. Compound 12 is reversible and specific for LSD1 as compared to the monoamine oxidases, shows minimal inhibition of CYPs and hERG, and inhibits proliferation and survival in several cancer cell lines, including breast and colorectal cancer. Compound 12 may be used to probe LSD1's biological role in these cancers.