  I explore the hypothesis that Ly$\alpha$ absorption at low redshift is caused
by the outer regions of extended galaxy disks, including those of dwarf and low
surface brightness galaxies. McGaugh (1996) has shown that the distribution of
central galaxy surface brightnesses may be flat to 25 B mag arcsec$^{-2}$ or
fainter. A population of galaxies is simulated based upon observed
distributions. The low-redshift neutral column density distribution is
predicted, and an estimate is made for the number density of disk galaxies
required to explain all absorbers. Results relating to galaxy luminosities and
impact parameters are discussed.
