Perovskite solar cells utilize solution-processed CH3NH3PbI3 thin films as the active layer material, whose morphology and exposed facets directly contribute to the device efficiency and stability. We investigated various conditions for growing CH3NH3PbX3 (X = Br, I) crystals from solutions, and found that bromide, nonaqueous solvents, and higher X-/PbX2 ratios favor the growth of cuboids over dodecahedra. We propose that these factors promote the coordination of X- to Pb2+ on the growing surfaces, thus making the {111}(c) faces outgrow the {100}(c) faces.