A consent to treatment form provides required information that a patient may use to give intelligent, informed consent to proposed treatment. This study applied two standard techniques to assess the degree to which 60 informed consent forms from five national cancer clinical trial groups were readable and understandable by patients. The forms were found slightly less difficult to comprehend than medical journals but substantially more difficult than comparable materials from the popular press. Three of four passages describing treatment methods, procedures, discomforts, and risks required a college level or greater reading ability to comprehend. Informed consent documents may not be understood by a substantial portion of patients who sign them. The very regulations designed to ensure a patient's informed cooperation with treatment may inadvertently lead to forms that are so complex as to make informed cooperation virtually impossible.