Giovannella, S (reprint author), Ist Nazl Fis Nucl, Lab Nazl Frascati, POB 13, I-00044 Frascati, Italy.
We report the first observation of the rare eta -> e(+)e(-)e(+)e(-)(gamma) decay based on 1.7 fb(-1) collected by the KLOE experiment at the DA Phi NE phi-factory. The selection of the e(+)e(-)e(+)e(-) final state is fully inclusive of radiation. We have identified 362 +/- 29 events resulting in a branching ratio of (2.4 +/- 0.2(stat+bckg) +/- 0.1(syst)) x 10(-5). (C) 2011 Elsevier B.V. All rights reserved.