  We report the discovery of millisecond pulsations from the low-mass X-ray
binary HETE J1900.1-2455 which was discovered by the detection of a type I
X-ray burst by the High Energy Transient Explorer 2 (HETE-2). The neutron star
emits coherent pulsations at 377.3 Hz and is in an 83.3 minute circular orbit
with a companion with a mass greater than 0.016 solar masses and likely less
than 0.07 solar masses. The companion star's Roche lobe could be filled by a
brown dwarf with no need for heating or non-standard evolution. During one
interval with an unusually high X-ray flux, the source produced quasiperiodic
oscillations with a single peak at 883 Hz and on subsequent days, the
pulsations were suppressed. We consider the distribution of spin versus orbital
period in neutron star low-mass X-ray binaries.
