This study investigated the mandibular height reduction in relationship to aging and the length of edentulism period. Data were collected from 120 edentulous male subjects (complete denture wearers) who were divided into two resorptive age groups. The edentulism period of the subjects was classified as 1 to 5, 5 to 10, and over 10 years. Ridge resorption was estimated on the panoramic radiograph by estimating the original height of the alveolar process as being three times the distance from the inferior border of the mandible to the inferior edge of the mental foramen. According to statistical analysis, the amount of mandibular height reduction increased in the older age group. The mandibular resorption rate was greatest in the earlier stages of edentulism and slowed with longevity of edentulism.