Osteopontin (SPP1) is a soluble ligand with pleomorphic immunologic activities including activation of macrophage chemotaxis, promotion of Th1 responses, and activation of B1 B cells. It has been implicated in the development of murine lupus and is overexpressed in humans with systemic lupus erythematosus (SLE). We examined a polymorphism of osteopontin for an association with lupus in humans in an effort to determine whether there is any evidence that a genetic predisposition to altered osteopontin expression might explain the overexpression seen in human SLE patients. A silent polymorphism (707C>T, rs1126616) of osteopontin was significantly associated with SLE. Additional associations with renal disease and opportunisitic infections were suggested. This is the first phenotypic association with a polymorphic variant of osteopontin. © 2002 Wiley-Liss, Inc.