Euphorbia deflexa, an endemic spurge from Greece, was investigated for the occurrence of its diterpene constituents. Through continuous monitoring by 1H NMR, 22 diterpenoids were isolated, including 16 previously undescribed compounds (euphodeflexins A-P), which belong to the jatrophane, ingenane, segetane, and pepluane diterpene types. Their chemical structures were elucidated through a combination of HRESIMS, NMR spectroscopy, and X-ray data. The isolated diterpenoids were tested against a panel of human cancer cell lines, as well as against two bacterial strains. Compounds 1, 13, and 17 were active against the HeLa cell line with IC50 values 9.9, 9.8, and 5.8 μM, respectively.