In this chapter, we illustrate the application of R to analyze adverse events (AEs) in clinical trials. Similarly to other chapters, we introduce clinical trial data in Section 11.1 and present the statistical models using confidence interval and significance level methods to analyze this type of data in Section 11.2. In Section 11.3, we show step-by-step implementation using the R system to analyze AE data. Concluding remarks appear in Section 11.4. Much of the material in this chapter appears in Chapter 17 in our book Peace and Chen (2010). Readers may refer to that book for more detailed descriptions of the data and methods.