Abstract Reliability of muscle thickness assessed in B-mode ultrasound has been confirmed in adults but remains a less direct assessment of muscle mass than muscle volume (MV). The aim of this prospective monocentric study was to assess the interday reliability of MV determined by the 2D-panoramic ultrasound in older hospitalized patients. Ten participants hospitalized in geriatric ward (mean age = 84) underwent 2 sessions of panoramic ultrasound scanning 1 week apart for MV assessment and DXA for leg lean mass (LLM) assessment when it was possible. The interday reliability of MV assessed using the intraclass correlation coefficient (ICC) was excellent, whatever was the muscle analyzed: ICC = 0.99 for tibialis anterior; ICC = 0.99 for vastus lateralis; ICC = 1 for rectus femoris. The pilot analysis of its association with leg lean mass revealed a good association between the vastus lateralis MV and LLM, but this needs to be confirmed on a larger number of participants (Pearson correlation coefficient = 0.91, P = 0.03). The 2D-panoramic ultrasound system for the determination of MV was reliable in older hospitalized patients with measurements performed on the patient's bed. MV seemed to be more correlated to LLM than muscle thickness. Future research will need to reduce the data processing time maybe with automation of data measurement.