We present the first time-resolved spectroscopic study of the cataclysmic variable DW Cancri .
We have determined an orbital period of 86.10 \pm 0.05 min , which places the system very close to the observed minimum period of hydrogen-rich cataclysmic variables .
This invalidates previous speculations of DW Cnc being either a permanent superhumper below the period minimum or a nova-like variable with an orbital period longer than 3 hours showing quasi-periodic oscillations .
The Balmer and He i lines have double-peaked profiles and exhibit an intense S-wave component moving with the orbital period .
Remarkably , the Balmer and He i radial velocity curves are modulated at two periods : 86.10 \pm 0.05 min ( orbital ) and 38.58 \pm 0.02 min .
The same short period is found in the equivalent width variations of the single-peaked He ii \lambda 4686 line .
We also present time-resolved photometry of the system which shows a highly-coherent variation at 38.51 min , consistent with the short spectroscopic period .
The large number of similarities with the short-period intermediate polar V1025 Cen lead us to suggest that DW Cnc is another intermediate polar below the period gap , and we tentatively identify the photometric and spectroscopic 38 min signals with the white dwarf spin period .
DW Cnc has never been observed to undergo an outburst , but it occasionally exhibits low states \sim 2 mag fainter than its typical brightness level of V \simeq 14.5 , resembling the behaviour of the high mass-transfer VY Scl stars .