Measurement of lateral rotation range of motion (ROM) is frequently performed during shoulder evaluation. The purpose of this study was to determine the intratester and intertester reliability of goniometric measurement of passive lateral rotation ROM of the shoulder. Two experienced PTs performed the testing in a randomized block design. They were blinded to all clinical information and to their goniometric readings. Passive lateral rotation ROM of the shoulder was assessed in 34 patients with a variety of shoulder pathologies. Patients were placed in the supine position with the arm abducted approximately 20 degrees to 30 degrees. A standard goniometer, placed along the joint axis by the therapist, was red by an independent assistant. Intraclass correlation coefficients (ICCs) and their associated 95% confidence intervals were calculated. Intratherapist ICCs (0.88 and 0.93) and intertherapist ICCs (0.85 and 0.80) were high. These findings suggest that reliable measures of passive lateral rotation ROM of the shoulder can be obtained from patients with shoulder pathology using standard goniometry and by placing the patient in a supine position.