  We have retrieved multicolor WFPC2/HST data from the STScI archive for 27
nearby Massive (>= 3x10^4 M_Sun) Young (< 20 Myr) star Clusters (MYCs). The
data represents the most-complete-to-date sample of clearly resolved MYCs. We
have analyzed their structural properties and have found that they can be
classified as either Super Star Clusters (SSCs) or as Scaled OB Associations
(SOBAs). SSCs have a compact core possibly surrounded by a halo while SOBAs
have no core. A morphological sequence can be established from SSCs with weak
halos to SSCs with strong halos to SOBAs and we propose that this is linked to
the original mass distribution of the parent giant molecular clouds. Our
results indicate that a significant fraction of the stars in MYCs dissipate on
timescales of 10 Gyr or less due to the extended character of some of the
clusters. Also, SSCs with ages < 7 Myr have smaller cores on average than those
with ages > 7 Myr, confirming predictions of numerical simulations with mass
loss.
