The "Morbidity and Mortality Weekly Report" ("MMWR") Series is prepared by the Centers for Disease Control and Prevention (CDC). Data presented by the Notifiable Disease Data Team and 122 Cities Mortality Data Team in the weekly "MMWR" are provisional, based on weekly reports to CDC by state health departments. This issue of "Morbidity and Mortality Weekly Report" includes the following reports: (1) Current Tobacco Use Among Middle and High School Students--United States, 2011 (Rene A. Arrazola, Shanta R. Dube, and Martha Engstrom); (2) Interim Guidance for Clinicians Considering the Use of Preexposure Prophylaxis for the Prevention of HIV Infection in Heterosexually Active Adults (DK Smith, Michael C. Thigpen, Steven R. Nesheim, Margaret A. Lampe, Lynn A. Paxton, Taraz Samandari, Amy Lansky, Jonathan Mermin, and Kevin Fenton); (3) Update to CDC's "Sexually Transmitted Diseases Treatment Guidelines," 2010: Oral Cephalosporins No Longer a Recommended Treatment for Gonococcal Infections (Carlos del Rio, Geraldine Hall, King Holmes, Edward W. Hook, Robert D. Kirkcaldy, Kimberly A. Workowski, Sarah Kidd, Hillard S. Weinstock, John R. Papp, David Trees, Thomas A. Peterman, and Gail Bolan); and (4) Vital Signs: Walking Among Adults--United States, 2005 and 2010 (David Berrigan, Dianna D. Carroll, Janet E. Fulton, Deborah A. Galuska, David R. Brown, Joan M. Dorn, Brian Armour, and Prabasaj Paul). Announcements and QuickStats are also included. Individual reports contain figures, tables and references.