In 2011, there were 1,355 retail clinics in the United States; this number is expected to more than double to 2,854 by 2018, according to a report from GBI Research. In addition, the number of patients visiting retail clinics has jumped from 1.48 million in 2006 to 5.97 million in 2009 — more than a fourfold increase, according to a study published in Health Affairs.