  The nucleus of the Seyfert galaxy NGC 1068 is believed to host a supermassive
black hole. Evidence for the presence of a massive central object is provided
by water maser emission, which displays a linear pattern in the sky, suggestive
of a rotating disk. The rotating disk hypothesis is further strengthened by the
declining shape of the derived rotation curve. Similar maser emission from NGC
4258 has led to a reliable estimate of the mass of the central black hole,
because in this case the rotation curve is Keplerian. In the case of NGC 1068
the rotation curve traced by the water maser is non-Keplerian. In this paper we
provide an interpretation of the non-Keplerian rotation in NGC 1068 by means of
a self-gravitating accretion disk model. We obtain a good fit to the available
data and derive a black hole mass M_{bh}=(8.0\pm 0.3) 10^6M_{sun}. The
resulting disk mass is comparable to the black hole mass. As an interesting
by-product of our fitting procedure, we are able to estimate the viscosity
parameter, which turns out to be \alpha\approx 10^{-2}, in line with some
theoretical expectations.
