  We present the results from coordinated X-ray observations of the
ultraluminous X-ray source NGC 5204 X-1 performed by NuSTAR and XMM-Newton in
early 2013. These observations provide the first detection of NGC 5204 X-1
above 10 keV, extending the broadband coverage to 0.3-20 keV. The observations
were carried out in two epochs separated by approximately 10 days, and showed
little spectral variation, with an observed luminosity of Lx = (4.95+/-0.11)e39
erg/s. The broadband spectrum confirms the presence of a clear spectral
downturn above 10 keV seen in some previous observations. This cutoff is
inconsistent with the standard low/hard state seen in Galactic black hole
binaries, as would be expected from an intermediate mass black hole accreting
at significantly sub-Eddington rates given the observed luminosity. The
continuum is apparently dominated by two optically thick thermal-like
components, potentially accompanied by a faint high energy tail. The broadband
spectrum is likely associated with an accretion disk that differs from a
standard Shakura & Sunyaev thin disk.
