The adduct formation in the reactions of Cl and Br atom with dimethyl sulfide (DMS) is studied theoretically and experimentally. The rate constants of the forward reaction at several temperatures and pressures are determined from the rise and decay time profiles of the adduct, Cl-DMS, using cavity ring-down laser spectroscopy. The high-pressure limit rate constant for the Cl-DMS adduct formation is determined to be k(1a)(high) = (2.2 +/- 0.2) X 10(-10) cm(3) molecule(-1) s(-1). The rate constant of Cl with DMS at atmospheric pressure is k(1) = (3.6 +/-0.2) x 10(-11) cm(3) molecule(-1) s(-1). Error bars are 1sigma. The Arrhenius plot of the forward reaction has a negative temperature dependence for 278-318 K. The calculated equilibrium constants of the reaction Cl and Br with DMS at 300 K are K-CIDMS = 2.8 x 10(-12) and K-BrDMS = 7.7 x 10(-15) cm(3) molecule(-1), respectively. The binding energy (D-0) is calculated to be 17.7 kcal mol(-1) for Cl-DMS, and 14.1 kcal mol(-1) for Br-DMS. D-0(Br-C) is in fair agreement with the previously reported experimental value, 12 +/- 1 kcal mol(-1). The results are discussed in comparison with previous experimental reports of the bromine atom adduct, Br-DMS. Atmospheric implications regarding the fate of the X-DMS adducts (X = Cl and Br) in the troposphere are discussed.