Context: Physical therapists often have to measure ankle range of motion (ROM) to decide on intervention and investigate improvements. The most common method of measurement is goniometry, but it has been questioned due to its unsatisfactory levels of reliability. Objective: To investigate the intraobserver and interobserver reliability of a new method of measuring plantar-flexion ROM. Design: Prospective and descriptive. Setting: Laboratory. Participants: 20 healthy participants (12 women and 8 men). Main Outcome Measurements: Ankle plantar flexion was measured by 3 observers (A, B, and C) with 3 methods (goniometry, measurement in hook-lying position [MHP], and static-image analysis [SIA]). Observer A was the most experienced therapist, and C, the least. MHP was performed with the participant in the supine position, knees flexed, and first and fifth metatarsals in contact with the treatment table. SIA was recorded and analyzed in the same position. Goniometry was performed with participant seated, lower legs unsupported, and axis positioned on the lateral malleolus. Results: For the interobserver analysis, the ICC2,1 was high for the MHP (.88), high for SIA (.87), and moderate for goniometry (.57). For the intraobserver analysis, the ICC2,1 was high or very high for MHP (.91-.92), high for SIA (.79-.83), and low to moderate for goniometry (.18-.60). Conclusion: MHP is inexpensive, fast, and more reliable than goniometry for measuring plantar-flexion ROM.