The structures and relative stabilities of (MgCl2)(n) sheetlike clusters and nanoballs were studied by quantum chemical methods. The sheets as discrete molecules were studied up to Mg100Cl200. Their stabilities increase systematically as a function of the size of the sheet. Periodic ab initio calculations were performed for (001) monolayer sheets of alpha- and beta-MgCl2, beta-sheet being slightly favored. Nanoballs were constructed from Archimedean polyhedra, producing tetrahedral, octahedral, and icosahedral symmetries, and were studied up to Mg60Cl120. Nanoballs prefer to take the shape of truncated cuboctahedron (Mg48Cl96). Comparisons to sheetlike clusters and periodic calculations suggest that magnesium dichloride nanoballs are stable.