Models were used to simulate the pre-focal tissue distributions encountered when treating intra-pelvic tumors with magnetic resonance guided high intensity focused ultrasound (MRgHIFU). Focal peak temperature and thermal dose volumes were considerably affected by depth and fat thickness. Exposures of 300 W for ≥20 s (≥6 kJ) were required to generate measurable 30EM dose contours 8 cm deep (6 cm pre-focal fat). The relative distributions of fat and muscle layers had minimal effect on focal heating, but influenced location of potentially damaging pre-focal heating. MRgHIFU treatments to deep-seated intra-pelvic tumors require methods for improving dose delivery at depth.