Accurate noninvasive clinical tests of shoulder instability are important in assessing and planning treatment for glenohumeral joint instability. An interexaminer agreement trial was undertaken to estimate the reliability of commonly used clinical tests for shoulder instability. Thirteen patients with a history suggestive of instability, who had been referred to a shoulder specialist for treatment of their symptomatic shoulders, were examined by four examiners of differing experience. Good to excellent interexaminer agreement was found for most variations of the load-and-shift test, with the best agreement in the 90 degrees abducted position for the anterior direction (intraclass correlation coefficient [ICC] = 0.72) and in the 0 degrees abducted position for the posterior (ICC = 0.68) and inferior (ICC = 0.79) directions. Fair to good interexaminer reliability was found for the sulcus sign (ICC = 0.60). With regard to the provocative tests, agreement was best when apprehension was used as the criterion for a positive test and was better for the relocation (ICC = 0.71) and release tests (ICC = 0.63) than for the apprehension (ICC = 0.47) and augmentations tests (ICC = 0.48). Reliability was poor (ICC < 0.31) when pain was used as the criterion for a positive test. These results indicate that the load-and-shift, sulcus, and provocative tests (apprehension, augmentation, relocation, and release) are reliable clinical tests for instability in symptomatic patients when care is taken with respect to arm positioning and if apprehension is used as the criterion for a positive provocative test.