Cis-hex-3-ene-1,5-diyne was synthesized using a Negishi coupling of two equivalents of trimethylsilyl acetylene to cis-dichloroethylene followed by the removal of the protecting trimethylsilane groups with t-butylammonium fluoride.  The resulting cis-ene-diyne decomposed quickly as a room temperature liquid, but the vapor was stable for weeks in a lecture bottle.  The infrared spectrum of cis-hex-3-ene-1,5-diyne in a low-temperature argon matrix consisted of thirteen vibrational bands and two strong overtone vibrations.  The photoreactivity of gas phase cis-hex-3-ene-1,5-diyne using the 254 nm line of a mercury arc lamp rapidly produced the trans isomer.  Photoirradiation of solid cis-hex-3-ene-1,5-diyne at 20 K produced the trans isomer along with at least one other significant photoproduct as identified by infrared spectroscopy.