  We present the results of five years (2005-2009) of MAGIC observations of the
BL Lac object PG 1553+113 at very high energies (VHEs). Adding the new data set
(2007-2009) to previous observations, this source becomes one of the best
long-term followed sources at energies above 100 GeV. In the last three years
of data, the flux level above 150 GeV shows a marginal variability.
Simultaneous optical data also show only modest variability that seems to be
correlated with VHE gamma-ray variability. We also performed a temporal
analysis of all available Fermi/LAT data of PG 1553+113 above 1 GeV. Finally,
we present a combination of the mean spectrum measured at VHE with archival
data available for other wavelengths. The mean Spectral Energy Distribution
(SED) can be modeled with a one-zone SSC model, which gives the main physical
parameters governing the VHE emission in the blazar jet.
