The authors have developed a noninvasive head immobilization system for use in neuroimaging (magnetic resonance imaging, computerized tomography, single photon emission computerized tomography, and projection angiography), neurosurgical planning, and neurosurgery. These diagnostic and surgical procedures require patient immobilization, reproducible patient positioning, and anatomical localization. The thermoplastic system described in this technical note addresses each of these requirements with a high degree of accuracy and with no bone fixation. The reproducibility of positioning and effectiveness of immobilization were evaluated using nine healthy volunteers during repeated sessions of magnetic resonance imaging. The mean axial displacement for repeated positioning was 0.6 mm (variance 0.1 mm); the mean displacement during robust patient motion in the axial direction was 1.8 mm (variance 0.9 mm).