We employ the full-potential linearized augmented plane wave plus local orbital (FP-L/APW + lo) method based on spin-polarized density functional theory (DFT) in order to investigate the structural, electronic and magnetic properties of ordered dilute ferromagnetic semiconductors Zn1?xCrxS and Cd1?xCrxS (x = 0.25) in the zinc blende (B3) phase. For the exchange-correlation functional, the generalized gradient approximation GGA (Wu-Cohen 06) has been used. Results of calculated electronic band structures and density of states of these dilute magnetic semiconductors (DMSs) are discussed in terms of the contribution of Cr 3d5 4s1, Zn 3d10 4s2, Cd 4d10 5s2 and S 3s2 3p4 partial density of states. For Cr-based systems without n or p-type doping, the stability of the ferromagnetic spin state versus the antiferromagnetic state is predicted. Band structure and density of states studies show half-metallic ferromagnetic nature for both alloys, Zn1?xCrxS and Cd1?xCrxS. Calculations of the s–d exchange constant N0? and p–d exchange constant N0? clearly indicate the magnetic nature of these compounds. From the calculated total magnetic moments we observe that p–d hybridization reduces the local magnetic moment of Cr from its free space charge value and produces small local magnetic moments on the nonmagnetic Zn, Cd and S sites. The robustness of half-metallicity of Zn1?xCrxS and Cd1?xCrxS as a function of lattice constant is also discussed.