ABSTRACTIntroduction: The primary aim of this investigation was to determine whether use of write‐zoom magnification affects sonographically determined cross‐sectional area (CSA) of peripheral nerves. Methods: CSAs of the median (MN) and posterior interosseous (PIN) nerves were measured in 22 limbs from 11 asymptomatic volunteers using both standard imaging and write‐zoom magnification. CSA measurements were repeated on the same images 1 week later. Results: The average CSA of write‐zoomed images for the MN was significantly larger at both measurement sessions (week 1: 11.1 mm2 write‐zoom vs. 10.0 mm2 standard, P = 0.019; week 2: 11.8 mm2 vs. 10.4 mm2, P = 0.023). Similar differences were noted for the PIN (week 1: 2.3 mm2 vs. 1.9 mm2, P = 0.002; week 2: 2.5 mm2 vs. 1.9 mm2, P = 0.001). Conclusions: Write‐zoom magnification may significantly increase the measured CSA of peripheral nerves. These changes appear to be more substantial when smaller nerves are measured. Muscle Nerve 51: 30–34, 2015