  New HI images from the VLA Galactic Plane Survey (VGPS) show clear absorption
features associated with the supernova remnant (SNR) G18.8+0.3. High-resolution
$^{13}$CO images reveal that molecular clouds overlap the radio filaments of
G18.8+0.3. The $^{13}$CO emission spectrum over the full velocity range in the
direction of G18.8+0.3 shows two molecular components with high
brightness-temperatureand three molecular components with low
brightness-temperature, all with respective HI absorption. This implies that
these clouds are in front of G18.8+0.3. In the HI images, the highest velocity
absorption feature seen against the continuum image of G18.8+0.3 is at 129 km
s$^{-1}$, which corresponds to the tangent point in this direction. This yields
a lower distance limit of 6.9 kpc for G18.8+0.3. Absence of absorption at
negative velocities gives an upper distance limit of 15 kpc. The broadened
profile at 20$\pm$5 km s$^{-1}$ in the $^{13}$CO emission spectra is a strong
indicator of a possible SNR/CO cloud interaction. Thus, G18.8+0.3 is likely to
be at the distance of about 12 kpc. The upper mass limit and mean density of
the giant CO cloud at 20$\pm$5 km s$^{-1}$ are \sim 6 \times 10^{5} M_{\odot}
and \sim 2 \times 10^{2} cm^{-3}. We find an atomic hydrogen column density in
front of G18.8+0.3 of $N_{HI}$ \sim 2 \times 10^{22} cm^{-2}. The ROSAT PSPC
observations show a diffuse X-ray enhancement apparently associated with part
of the radio shell of G18.8+0.3. Assuming an association, the unabsorbed flux
is 2.2 \times10^{-12} erg cm^{-2} s^{-1}, suggesting an intrinsic luminosity of
3.6 \times 10^{34} erg s^{-1} for G18.8+0.3.
