We present new observations of a transit of the 111.4-day-period exoplanet HD80606b. Due to this long orbital period and to the orientation of the eccentric orbit (e=0.9), the HD80606b's transits last for about 12 hours. This makes practically impossible the observation of a full transit from a given ground-based observatory. Using the Spitzer Space Telescope and its IRAC camera on the post-cryogenic mission, we performed a 19-hour-long photometric observation of HD80606 that covers the full transit of 13-14 January 2010 as well as off-transit references immediately before and after the event. We complement this photometric data by new spectroscopic observations that we simultaneously performed with SOPHIE at Haute-Provence Observatory. This provides radial velocity measurements of the first half of the transit that was previously uncovered with spectroscopy.