Abstract
We present radio continuum and recombination line observations of 16 UCH II regions with large ratios of single-dish to VLA fluxes. All the sources but one are physically associated with extended emission. The UCH II regions and their extended envelopes are likely to be excited by the same ionizing sources. Therefore, almost all the observed UCH II regions are not likely to be real UCH II regions but ultracompact cores of more extended H II regions. We consider the origin of extended emission and discuss its implications on the age problem of UCH II regions.
