  Gauge Mediated Supersymmetry Breaking (GMSB) models provide a possible
mechanism to mediate Supersymmetry to the visible sector. In these models the
lightest supersymmetric particle (LSP) is usually the gravitino, while the
next-to-lightest supersymmetric particle (NLSP) is either a neutralino or a
slepton. In the case of a stau NLSP events with large missing transverse
energy, highly energetic jets and up to four $\tau$ leptons are expected in
$pp$-collisions at the LHC. A study of the expected performance of the ATLAS
detector in GMSB scenarios with a stau NLSP for a LHC center-of-mass energy of
$\sqrt{s}$ = 10 TeV is presented. A cut-based selection has been optimised
using a typical GMSB scenario and a scan of the GMSB parameter space has been
performed to determine the discovery reach as a function of the integrated
luminosity. In addition, the invariant mass distribution of two $\tau$ leptons
has been used to study the measurement of masses of supersymmetric particles
with larger event samples.
