We present deep BVRI band images and H I line observations of the nearby, low surface brightness galaxy ESO 215-G?009, which were obtained with the Australian National University 2.3 m telescope and the Australia Telescope Compact Array, respectively. ESO 215-G?009 was selected from the HIPASS Bright Galaxy Catalog because it has the second highest H I mass-to-light ratio of the galaxies with measured B-band apparent magnitudes. We find that it is an isolated dwarf irregular galaxy with an old stellar population. We place an upper limit on the current star formation rate of ∼2.5x10–3 M☉/yr. The extended H I disk shows regular rotation (vrot=51±8 km/s) and, at a column density of ∼5.0x1019 atoms/cm2, can be traced out to over 6 times the Holmberg radius of the stellar component (radius at µB=26.6 mag/arcsec2). After foreground star subtraction, we measure a B-band apparent magnitude of 16.13±0.07 mag within a radius of 80". The H I flux density is 122±4 Jy km/s within a radius of 370". Given a Galactic extinction of AB=0.95±0.15 mag, we derive an H I mass-to-light ratio of 22±4 M☉/L_☉,B_for ESO 215-G?009. To our knowledge this is the highest MHI/LBratio for a galaxy to be confirmed by accurate measurement to date.