OBJECTIVE To investigate the ultrasonographic anatomy of the lower leg for safe and accurate needle placement into the tibialis posterior using the anterior approach. METHODS Cross-sectional study. METHODS University rehabilitation hospital. METHODS Healthy volunteers (N=62; 30 men, 32 women). METHODS Not applicable. METHODS The safety window (the tibia to the neurovascular bundle) and the depth to the midpoint of the safety window (skin to the tibialis posterior) at the upper third and the midpoint of the tibia were measured with a transverse ultrasonographic scan. RESULTS The safety window at the upper third of the tibia was significantly larger than that at the midpoint (P<.01). The safety window ranged from .64 cm to 2.13 cm at the upper third tibialis point and from .32 cm to 1.30 cm at the midpoint. The depth to the tibialis posterior at the upper third of the tibia was significantly deeper than that in the midpoint (P<.01). The depth ranged from 2.47 cm to 4.66 cm at the upper third tibias point and from 2.35 cm to 4.28 cm at the midpoint. CONCLUSIONS Ultrasonography is a useful tool in measuring the safety window and the depth to the tibialis posterior using the anterior approach. Considering the safety window, we suggest the needle placement at the upper third point of tibia rather than that at the midpoint.