Scientifically validated (accurate), and reproducible (precise) methods of assessing the frequency and severity of patient symptoms are becoming more widely used in medicine. Such a symptom index has been developed for patients with benign prostatic hyperplasia, and may find use in clinical practice and research. The criteria for developing and validating such indexes are presented, using the new benign prostatic hyperplasia symptom index as an example. The same approach can be applied to many other disease entities in urology that demand a quantitation of the illness experience from the perspective of the patients.