  We derive the disk I-band luminosity function from the Zheng et al. sample of
\~1400 disk M dwarfs observed with the Hubble Space Telescope. We adopt a
Galactic-height-dependent color-magnitude relation to account for the
metallicity gradient above the Galactic plane. The resultant I-band luminosity
function peaks at M_I~9.5 and drops sharply toward M_I~10.5.
