  We present results of our diffraction-limited mid-infrared imaging of the
massive star-forming region W3(OH) with SpectroCam-10 on the 5-m Hale telescope
at wavelengths of 8.8, 11.7, and 17.9 micron. The thermal emission from heated
dust grains associated with the ultracompact HII region W3(OH) is resolved and
has a spatial extent of ~2 arcsec in the N band. We did not detect the hot core
source W3(H_2O) which implies the presence of at least 12 mag of extinction at
11.7 micron towards this source. These results together with other data were
used to constrain the properties of W3(OH) and W3(H_2O) and their envelopes by
modelling the thermal dust emission.
