Research Methods: This research analyzed the data on those aged 20 and older from the Report on Korean Medicine Usage Research, which was conducted in 2011. The definitions of toxicity were defined by the presence of toxicity listed in the survey. The questions used in analysis were sex, age, household income, health insurance, medical fees, satisfaction rates on treatments, as well as the types of diseases and the presence of toxicity from treatments. The analysis was done through frequency analysis using SAS 9.2 and Fisher's Exact Test. Results: Toxicity occurred in 2.1% patients out of the 3518 studied. The types of toxicity were skin problems, such as hives and pruritus (34.7%), gastrointestinal problems (20.8%), neurological diseases (4.2%), liver(1.4%), kidney toxicity(1.4%), and others (22.2%). There were no differences in toxicity by sex, age, household income and the types of health insurances. However, toxicity were positively correlated with the increase in standard of education (p=0.0124). In addition, as treatment costs increased (p<0.0001) and satisfaction rates decreased, toxicity increased (p<0.0001). Toxicity increased in patients with low back pain (p=0.0429), hwabyung (p=0.0392), lumbar sprain (p=0.0004), correction body type (p=0.0118), growth (p=0.0045), and from motor accidents (p=0.0448). In logistic regression analysis, Toxicity were positively correlated with medical fees, and cancer treatment and negatively correlated with satisfaction rate on treatments. Conclusion: The toxicity that occurred in outpatients who used Korean medical clinics mostly happened in skin, digestive organs, nerves, livers, and kidneys toxicity. The occurrences differed by the Educational lengths, expensive costs of treatments, low satisfaction rates of the treatments, and cancer.