We report photometry and spectroscopy of the outburst of the young stellar object ESO-Hα 99. The outburst was first noticed in Gaia alert Gaia18dvc and later by ATLAS. We have established the outburst light curve with archival ATLAS "Orange" filter photometry, Gaia data, new V -band photometry, and J, H, and K s photometry from IRIS and UKIRT. The brightness has fluctuated several times near the light curve maximum. The TESS satellite observed ESO-Hα 99 with high cadence during one of these minor minima and found brightness fluctuations on timescales of days and hours. Imaging with UKIRT shows the outline of an outflow cavity, and we find one knot of H 2 1−0 S(1) emission, now named MHO 1520, on the symmetry axis of this nebula, indicating recent collimated outflow activity from ESO-Hα 99. Its pre-outburst SED shows a flat FIR spectrum, confirming its early evolutionary state and its similarity to other deeply embedded objects in the broader EXor class. The pre-outburst luminosity is 34 L ⊙ , a much higher luminosity than typical EXors, indicating that ESO-Hα 99 may be a star of intermediate mass.Infrared and optical spectroscopy show a rich emission line spectrum, including H I lines, strong red Ca II emission, as well as infrared CO bandhead emission, all characteristic EXors in the broadest sense. Comparison of the present spectra with an optical spectrum obtained in 1993, presumably in the quiescent state of the object, shows that during the present outburst the continuum component of the spectrum has increased notably more than the emission lines. The Hα equivalent width during the outburst is down to one half of its 1993 level, and shock-excited emission lines are much less prominent. accretion phase, often show substantial variability due to instabilities in the accretion process. The accretion characteristics of young stars have recently been reviewed by Hartmann et al. (2016) and we follow their general line of discussion and the references therein.Traditionally, the photometric outbursts caused by increased accretion rates were divided by Herbig (1977) 2. ESO-Hα 99: CONTEXT AND PRE-OUTBURST PROPERTIES 1