We aimed to validate the Japanese version of the Aging Males' Symptoms rating scale (JPN-AMS) by using factor analysis. The study included 155 normal men 40 years old and older, and 116 patients who visited our clinic with complaints of aging males' symptoms. Participants self-administered the JPN-AMS. Factor analysis was done to confirm the internal structure of the questionnaire. We found three items that were not among the factors in the original Aging Males' Symptoms rating scale in normal men and seven items that were not the factors in the original scale in the patients who had a serum free testosterone level below 8.5 pg/ml. In particular, 5 of the 7 somatic items seemed not to be associated with the somatic factor. In conclusion, the factor analysis provided a confirmation of the internal structure of the JPN-AMS. We have to be aware of the different internal structure of the JPN-AMS for the Japanese patients with late-onset hypogonadism. Therefore, we should take care to use the JPN-AMS, as there are cultural differences among countries
