  We present simultaneous spectral and photometric observations of SDSS
J123813.73-033933.0. From Ha radial velocity measurements we determined the
orbital period of the system to be 0.05592+/-0.00002 days (80.53 min). The
spectrum shows double Balmer emission lines flanked by strong, broad
absorption, indicating a dominant contribution from the white dwarf. The
photometric light curve shows complex variability. The system undergoes cyclic
brightening up to 0.4 mag which are semi-periodical on short time scales with
periods of the order of 7-12 hours. We also detect 40.25 min variability (~0.15
mag) in the light curve, that corresponds to half the orbital period. Its
amplitude increases with the cyclic brightening of the system.
