We present the first observation of the decay K-S -> pi (+)pi (-)e(+)e(-) b
ased upon the data collected in 1998 by the NA48 experiment at CERN. We hav
e identified a clean sample of 56 events with negligible background contami
nation. Using K-L -> pi (+)pi (-)pi (0)(D) decays as normalization sample,
the branching ratio is measured to be BR(K-S -> pi (+)pi (-)e(+)e(-)) = [4.
5 +/- 0.7(stat) +/- 0.4(syst)] x 10(-5). This result is in good agreement w
ith the theoretical expectations from the mechanism of inner bremsstrahlung
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