  We present an experimental and theoretical study of atom-molecule collisions
in a mixture of cold, trapped atomic nitrogen and NH molecules at a temperature
of $\sim 600$~mK. We measure a small N+NH trap loss rate coefficient of
$k^{(\mathrm{N+NH})}_\mathrm{loss} = 8(4) \times 10^{-13}$~cm$^{3}$s$^{-1}$.
Accurate quantum scattering calculations based on {\it ab initio} interaction
potentials are in agreement with experiment and indicate the magnetic dipole
interaction to be the dominant loss mechanism. Our theory further indicates the
ratio of N+NH elastic to inelastic collisions remains large ($>100$) into the
mK regime.
