Ab initio all-electron quantum mechanical methods, including the Hartree-Fock (HF), second-order perturbation theory, configuration interaction with single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD) methods, have been applied to four arsenic clusters, diatomic As-2, tetrahedral As-4, cagelike As-12 belonging to the D-3d point group, and dodecahedral As-20. Several basis sets were used. The double-zeta plus polarization (DZP) includes both d and f polarization functions, while the triple-zeta plus double polarization basis includes two sets of f functions on each atom. From the most reliable theoretical results, As-12 is energetically lowest among the clusters considered, and As-20 is energetically comparable to AS(4).