The distal thigh atrophy is a frequently associated sigh in the presence of knee pathology, and it is usually proved by the difference of the distal thigh circumference using tapeline measurement. But the proper position of measurement is known at this moment. From January of 1988 to December of 1991, we have 320 patients who had knee problems. Among them, 50 patients were selected as a sample of this study. We measured distal thigh circumference of normal and abnormal side by patella and also real circumference and area by taking cross sectional C-T image at each point of measurement. The obtained data are analysed by SPSS for statistical treatment. And the results are as follows: 1) We notice the largest difference on the point of 10cm above superior pole of patella. 2) The vastus medialis is the most conspicuously atrophied muscle among quadriceps and the atrophy of hamstring is minimal. 3) We have experienced the largest difference in cruciate ligament injury but a little difference in meniscus pathology. 4) There is no significantly difference between tapeline measurement and real circumference. As a conclusion of study, The position of 10cm above from the patella upper pole is the best site of clinical measurement of distal thigh circumference, and the muscle mainly associated with artophy is vastus medialis.