The correlation consistent composite approach (ccCA) is reformulated utilizing a restricted open-shell reference wavefunction to remove spin-contamination from open-shell systems. The RO-ccCA-PS3 variant has an MAD of 0.65 kcal mol (1) for the 32 open-shell systems in the G3/99 enthalpy of formation test set, as compared to 0.77 kcal mol (1) using the unrestricted formulation. For the 22 most highly spin-contaminated species in the G3/99 test set, RO-ccCA produces a lower MAD; 1.20 versus 2.17 kcal mol (1). Additionally, the performance of RO-ccCA is examined for 30 bond dissociation energies and found to show improved accuracy over unrestricted ccCA. (C) 2011 Elsevier B. V. All rights reserved.