One of the most challenging assignments a court interpreter faces is interpreting for expert witnesses. Advances in science and technology over the last few decades and the 'beyond a reasonable doubt' standard have made the use of expert witnesses from a wide variety of fields a common practice in American courtrooms. It has generally been assumed that the testimony of an expert witness is challenging substantively but not formally. Preparation has focused on specialized vocabulary and phraseology. However, after reading several hundred pages of transcribed courtroom testimony the author saw that expert witness testimony from a number of different fields was not as lexically specialized as one would believe, but that it did contain many more grammatical, structural and syntactic errors than would be expected. In this study the author has classified the most frequently occurring errors found in this transcribed testimony, and has noted the strategies used by both novice and experienced interpreters to deal with these challenges.