The nonechogenic space between the bone and the joint capsule was measured in ultrasonographic scans at six different sites in 60 elbow joints of 30 healthy adults as well as in 35 joints with clinical arthritis. The space could be demonstrated in all healthy joints on the volar side at the levels of the trochlea and the capitulum of the humerus. The space was more than 2 mm in three out of the 60 healthy joints at these levels, and the space did not increase in 30 degrees flexion of the joint. The means of the measurements were significantly higher at all six sites in the arthritic joints than in the healthy joints and on the volar site the space increased in 30 degrees flexion of the arthritic joint. The space was more than 2 mm in all arthritic joints at the levels of either the trochlea or the capitulum of the humerus. An ultrasonographic distance of more than 2 mm on the volar side of the elbow joint between the joint capsule and the bone is with high probability a sign of intraarticular effusion or synovitis. The effusion in the olecranon fossa can also be demonstrated in all cases.