  We report the detection of a massive (M(gas) > 5x10^9 Msun) molecular/dusty
disk of 1.4kpc-size fueling the central engine of the Compact Symmetric Object
(CSO) 4C31.04 based on high-resolution (0.5''--1.2'') observations done with
the IRAM Plateau de Bure interferometer (PdBI). These observations allow for
the first time to detect and map the continuum emission from dust at 218GHz in
the disk of a CSO. The case for a massive disk is confirmed by the detection of
strong HCO+(1--0) line emission and absorption. The molecular gas mass of
4C31.04 is in the range 0.5x10^10--5x10^10Msun. While the distribution and
kinematics of the gas correspond roughly to those of a rotating disk, we find
evidence of distortions and non-circular motions suggesting that the disk is
not in a dynamically relaxed state. We discuss the implications of these
results for the general understanding of the evolution of radio galaxies.
