[en] We report the results of the CPLEAR experiment on CP-, T- and CPT-symmetries in the neutral kaon system. CP-violation parameters are given for different decay channels. For the first time T-violation is measured by a direct method using semileptonic decays. The CPT symmetry in the kaons decays is tested through the parameters Im(δ), from the Bell-Steinberger relation, with a precision of 10^-5 and Re(δ) with a precision of a few 10^-4 (two order of magnitude better than the previous measurement). These two measurements allow us to bound the difference in mass and width of K⁰ and K-bar⁰ to be equal within 10^-18 GeV. In the limit of CPT invariance in the neutral kaon decays, the K⁰ and K-bar⁰ masses are equal within 10^-19 GeV