The molecular electric quadrupole moment (Theta) of Cl-2 has been calculated using SDCI, and (SC)(2) -SDCI wave functions as well as CCSD, CCSD(T), and CC3 methods. All these correlation methods are single reference. All of them, but SDCI, are free of the size-extensivity error. The variation of Theta from the separated atoms to the equilibrium region is reported. The present results leads to an estimated value of 2.3520a.u. (10.55 x 10(-40) Cm-2) corresponding to a CC(3) calculation at the CBS approach and including the ro-vibrational and thermal averaging corrections. This value is compatible with two experimental values and points to one of them as slightly more reliable. (C) 2003 Elsevier B.V. All rights reserved.