  We report on a multiwavelength campaign on the radio-loud Narrow-Line Seyfert
1 (NLS1) Galaxy PMN J0948+0022 (z=0.5846) performed in 2010 July-September and
triggered by a high-energy gamma-ray outburst observed by the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope. The peak flux in
the 0.1-100 GeV energy band exceeded, for the first time in this type of
source, the value of 10^-6 ph cm^-2 s^-1, corresponding to an observed
luminosity of 10^48 erg s^-1. Although the source was too close to the Sun
position to organize a densely sampled follow-up, it was possible to gather
some multiwavelength data that confirmed the state of high activity across the
sampled electromagnetic spectrum. The comparison of the spectral energy
distribution of the NLS1 PMN J0948+0022 with that of a typical blazar - like 3C
273 - shows that the power emitted at gamma rays is extreme.
