We examined intratester and intertester reliability for goniometric measurements of ankle dorsiflexion (ADF) and ankle plantar flexion (APF) active range of motion (AROM). Parallel-forms intratester reliability for ankle AROM measurements obtained by the universal goniometer (UG) and by visual estimation (VE) and intertester reliability for VE of ADF and APF were examined. Repeated measurements were obtained on 38 patients with orthopedic problems by 10 physical therapists in a clinical setting. For intratester reliability of measurements obtained with UG, intraclass correlation coefficients (ICC) for all physical therapists were 0.64 to 0.92 (median, 0.825) for ADF and 0.47 to 0.96 (median, 0.865) for APF. Intertester reliability was quantified with use of ICC. ICCs for measurements obtained by UG were 0.28 for ADF and 0.25 for APF; ICC of VE for ADF was 0.34 and was 0.48 for APF. ICC for parallel-forms intratester reliability obtained with UG and VE ranged from 0 to 0.94 (median, 0.58) for ADF and 0 to 0.86 (median, 0.625) for APF. Thus, a physical therapist should use a goniometer when making repeated measurements of ankle joint AROM. Considerable inconsistency exists when two or more physical therapists make repeated goniometric and visual measurements of ankle motion on the same subject. Physical therapists may erroneously conclude that a patient's AROM has changed because of treatment when the change could be attributed to a lack of intertester reliability.