The aggregated structure of sodium dodecyl sulfate (SDS) adsorbed to the graphite-solution interface has been determined in the presence of the divalent ions : Mg2+, Mn2+, and Ca2+. Divalent ions are expected to alter the electrostatic interactions between charged headgroups and thus to cause changes from the structure formed with monovalent ions. However, atomic force microscopy reveals that the adsorbed structures are long (mu m) and thin (similar to 5 nm) and thus very similar in appearance to those observed in the presence of only monovalent counterions. Energetic considerations suggest that under most conditions the aggregates are hemicylinders, although not necessarily of constant curvature. When Mn2+ is added at constant low SDS concentration, the narrow dimension of the structure (the period) decreases linearly with solution Debye length down to a limiting period of about 5 nm. When Mg2+ is added at constant low SDS concentration, the period decreases slightly and then remains roughly constant. This suggests that the aggregate diameter increases. For both of these ions, force measurements suggests that there is a transition from a thin layer to a thicker layer as the divalent ion is added. At surfactant concentrations several times greater than the critical micelle concentration, the addition of divalent ions has no observable effect on the adsorption. We did not observe a transition to a flat layer at any of the conditions examined.