  We report optical, soft X-ray, and UV observations of the peculiar Seyfert
galaxy IC 3599 using data obtained with ROSAT and IUE. Most remarkably, we
discovered a rapid decrease of the X-ray flux by a factor of about 100 within
one year and a more gradual decrease thereafter. The X-ray spectrum of IC 3599
was soft at flux maximum and became even softer as the flux decreased.
Simultaneously with the late decrease of the X-ray flux, we observed a decrease
in the strength of highly ionized optical iron lines. We discuss several
explanations for this behaviour including an accretion disk instability and
tidal disruption of a star orbiting a central massive black hole.
