  We present phase resolved optical photometry and spectroscopy of the
accreting millisecond pulsar HETE J1900.1-2455. Our R-band light curves exhibit
a sinusoidal modulation, at close to the orbital period, which we initially
attributed to X-ray heating of the irradiated face of the secondary star.
However, further analysis reveals that the source of the modulation is more
likely due to superhumps caused by a precessing accretion disc. Doppler
tomography of a broad Halpha emission line reveals an emission ring, consistent
with that expected from an accretion disc. Using the velocity of the emission
ring as an estimate for the projected outer disc velocity, we constrain the
maximum projected velocity of the secondary to be 200 km/s, placing a lower
limit of 0.05 Msun on the secondary mass. For a 1.4 Msun primary, this implies
that the orbital inclination is low, < 20 degrees. Utilizing the observed
relationship between the secondary mass and orbital period in short period
cataclysmic variables, we estimate the secondary mass to be ~0.085 Msun, which
implies an upper limit of ~2.4 Msun for the primary mass.
