Introduction: The reduction of skeletal muscle mass that occurs with aging (sarcopenia) leads to disability in the elderly population. Purpose: To investigate the prevalence of sarcopenia among older frail nursing home residents and to examine the rate of change in muscle thickness (MT) over 12 months. Methods: B-scan ultrasound equipment with a 5MHz transducer was used to measure MT on 16 older frail women nursing home residents (age = 85.0 yr, height = 143.9 cm, mass 45.4kg) at six sites (triceps, biceps, subscapular, abdomen, quadriceps, and hamstrings). Sarcopenia was defined as 2 SD below the MT norm for Japanese young men and women (Abe and Fukunaga, 1995). Results: MT of quadriceps for all subjects was 2 SD below the normal MT of young adults at baseline. The prevalence of sarcopenia in triceps, biceps, abdomen, subscapular, and hamstrings was 25-93% at baseline. After 6 months of living in a nursing home, the prevalence of sarcopenia for the upper body and trunk increased (p < 0.05). Biceps and triceps MT decreased by 37% and 32%, respectively, after 12 months. Abdomen and subscapular MT decreased by 29% and 52%, respectively. Quadriceps and hamstrings MT decreased by 18% and 24%, respectively. Conclusion: Residing in a nursing home and maintaining an inactive lifestyle is associated with a decrease of upper limb and trunk MT that parallels the loss of muscle mass in the lower limbs. Future research should address interventions that attenuate this muscle loss.