The aim of this study was to evaluate two methods of clinical assessment for external rotation of the shoulder to optimise the diagnosis of hyperlaxity in patients being selected for surgery for stabilisation of chronic anterior instability. External rotation was evaluated in 70 healthy student volunteers by two examiners (intertester study) using two methods of assessment at 15-day intervals (intratester study). The first method used was the protocol described for the Instability Severity Index Score (ISIS). In this case, the subject was evaluated in the sitting position, bilaterally with passive range of motion movements. The shoulder was considered hyperlax if ER1 was greater than 85°. With the second, so-called “elbow on the table” (EOT) method, the subject was evaluated in the decubitus dorsal position, unilaterally with passive range of motion. The subject was considered to be hyperlax if ER1 was greater than 90°. Kappa values for intra- and intertester agreement with the ISIS method were average, while they were satisfactory with the intraclass coefficient (ICC). Kappa values for inter- and intratester agreement with the EOT method were average and good, respectively. This tendency was confirmed by the ICC which went from good to excellent for the two examiners in both series of measurements using the EOT method, showing better reproducibility with this method. Our study confirms that the most reproducible method for assessing external rotation is obtained by unilateral assessment of the patient in the decubitus dorsal position, with passive range of motion. An ER1 of 90° is the necessary threshold for hyperlaxity because of elbow retropulsion with this method, which provides immediate and visual evaluation and eliminates the necessity of goniometry.