The purpose of this research is to find out the mathematical equations and variables on the epidemiology of patients led epidemic retrospective and equations derived prediction and forecast the population was sick. The population was hospital outpatient of Thanyaburi since October 31, 2009 – September 30, 2013 include all patients 5,331. Registration information, history of the patient (OPD card) the database of hospital and data manipulation. With the principles data mining in order to the appropriate information and learn by GPdotNet V .3. To obtain a mathematical equation for forecasting (expected).