The carpal height index (carpal height ratio of the diseased wrist divided by that of the normal wrist, as described by Kato et al.) was calculated in forty normal subjects, ten patients who had Stage-III lunatomalacia, and eight patients who had non-union of a fracture of the scaphoid. The method of Youm et al. for determining the carpal height index was altered to include the use of defined points of reference and a standardized radiographic technique. Two tests of reproducibility demonstrated the reliability of the method. The carpal height index was found to be superior to the carpal height ratio for the evaluation of unilateral disease. The mean carpal height index of diseased wrists differed significantly from that of normal wrists. The carpal height index (for unilateral disease) or the carpal height ratio (for bilateral disease) can be used to describe the progression of collapse of the wrist quantitatively and to evaluate and compare various forms of treatment.