The purpose of the study is to correlate the sonographic signs of rotator cuff tears (RCTs) with surgical findings, with emphasis on partial-thickness tear. We prospectively performed ultrasonography (US) on 50 patients with suspected RCTs and comparison with operative findings. Six US signs, which included "nonvisualization", "focal depression", "focal thinning", "focal hypoechoic cleft", "floating bright spots" and "focal heterogeneous hypoechogenicity" in rotator cuffs (RCs), were emphasized, but only "focal heterogeneous hypoechogenicity" favored partial-thickness tear (10/14, 71%). All the other five signs, including "floating bright spots" (not pointed out in literatures), were suggestive of full-thickness tear. The overall sensitivity, specificity, positive predictive value, negative predictive value and accuracy for US to detect RCTs were 95%, 90%, 97%, 82% and 94%, respectively. US is effective to detect RCTs and differentiate full- from partial-thickness tear.