Abstract We present the first detection of ( Z )-1,2-ethenediol, (CHOH) 2 , the enol form of glycolaldehyde, in the interstellar medium toward the G+0.693−0.027 molecular cloud located in the Galactic Center. We have derived a column density of (1.8 ± 0.1) × 10 13 cm −2 , which translates into a molecular abundance with respect to molecular hydrogen of 1.3 × 10 −10 . The abundance ratio between glycolaldehyde and ( Z )-1,2-ethenediol is ∼5.2. We discuss several viable formation routes through chemical reactions from precursors such as HCO, H 2 CO, CHOH, or CH 2 CHOH. We also propose that this species might be an important precursor in the formation of glyceraldehyde (HOCH 2 CHOHCHO) in the interstellar medium through combination with the hydroxymethylene (CHOH) radical.