OBJECTIVES: We estimated the number of Korean workers with back pain and evaluated the populationbased factors associated with back pain from a representative sample. METHODS: The number of Korean workers who experienced back pain (back pain-experienced patients), those who had experienced back pain lasting for three or more months during the previous year (chronic patients), and those who were currently suffering from back pain (current patients) were estimated by analyzing the data from the fourth Korea National Health and Nutrition Examination Survey conducted in 2007 using the surveyfreq procedure of the SAS statistical package. Population-based odds ratios for being back pain-experienced, chronic, and current patient according to demographic (age, gender, and education), lifestyle (smoking, drinking, and exercise), and occupational (industrial class, employment status, occupation) factors were estimated using the surveylogistic procedure. RESULTS: Among 19,076,186 Korean workers aged 20~69 years in 2007, 2,473,997(proportion, 13.0%; 95% CI, 1,976,779~2,971,216) were estimated to be back pain-experienced patients, 692,046(3.6%; 417,726~966,366) chronic patients, and 1,206,704(6.3%; 893,475~1,519,933) current patients. Each of the explanatory variables was significantly associated with at least one of the response variables for back pain. CONCLUSIONS: Further efforts to investigate the epidemiology of back pain, evaluate the associated factors, and improve treatment outcomes are needed.