The Longissimus thoracis et lumborum muscle (LM) volume was measured in vivo by real-time ultrasonography (RIU) in 13 female sheep. Animals were scanned over 6 identified sites (7th, 9th, II th and 13th thoracic vertebrae and 2nd and 4th lumbar vertebrae). After RID measurements, the animals were weighed and slaughtered. RTU volume measurements were calculated by multiplying the LM area obtained at each site by the slice lengths. Equivalent measurements to those taken in vivo were obtained on the carcass using a digital camera and image analysis software. Correlation analysis was carried out to evaluate relationships between LM volume measured in vivo by RTD and in carcass. The LM volume measured in carcass and in vivo by RTD was highly correlated (r= 0.96, 0.96 and 0.98 for lumbar, thoracic and all vertebrae, respectively). These results strongly support that LM volume can be predicted in vivo by RTU.