University of California, San Francisco (Coordinating Center): S. R. Cummings (principal investigator), M. C. Nevitt (coinvestigator), D. C. Bauer (coinvestigator), K. Stone (project director), D. M. Black (study statistician), H. K. Genant (director, central radiology laboratory), P. Mannen (research associate), T. Blackwell, W. S. Browner, M. Cockrell, T. Duong, C. Fox, S. Harvey, M. Jaime-Chavez, L. Y. Lui, G. Milani, L. Nusgarten, L. Palermo, E. Williams, D. Tanaka, and C. Yeung. University of Maryland, Baltimore: M. Hochberg (principal investigator), J. C. Lewis (project director), D. Wright (clinic coordinator), R. Nichols, C. Boehm, L. Finazzo, B. Hohman, T. Page, S. Trusty, H. Kelm, T. Lewis, and B. Whitkop. University of Minnesota, Minneapolis: K. Ensrud (principal investigator), K. Margolis (coinvestigator), P. Schreiner (coinvestigator), K. Worzala (coinvestigator), M. Oberdorfer (project director), E. Mitson (clinic coordinator), C. Bird, D. Blanks, F. Imerker-Witte, K. Jacobson, K. Knaught, N. Nelson, E. Penland-Miller, and G. Saecker. University of Pittsburgh, Pittsburgh, Pa: J. A. Cauley (principal investigator), L. H. Kuller (coprincipal investigator), M. Vogt (coinvestigator), L. Harper (project director), L. Buck (clinic coordinator), C. Bashada, D. Cusick, G. Engleka, A. Flaugh, A. Githens, M. Gorecki, D. Medve, M. Nasim, C. Newman, S. Rudovsky, N. Watson, and D. Lee. The Kaiser Permanente Center for Health Research, Portland, Ore: T. Hillier (principal investigator), E. Harris (coprincipal investigator), E. Orwoll (coinvestigator), H. Nelson (coinvestigator), Mikel Aiken (biostatistician), Marge Erwin (project administrator), Mary Rix (clinic coordinator), Jane Wallace, Kathy Snider, Kathy Canova, Kathy Pedula, and Joanne Rizzo.