Background: Total hip resurfacing has become increasingly popular over the last decade. There remains concern about the effect of the surgical approach on femoral head viability and the role of resurfacing in the management of established osteonecrosis. In view of these concerns, we examined femoral head viability following resurfacing through a modified anterolateral approach. Methods: The viability of the femoral heads of ten patients who had undergone successful unilateral Birmingham hip resurfacing was assessed with use of positron emission tomography in conjunction with the injection of fluorine at a mean of twenty months after surgery. For each patient, in both the hip that had undergone resurfacing and the contralateral nonresurfaced hip, activity was measured in four regions of interest: the lateral aspect of the femoral head, the medial aspect of the femoral head, the lateral aspect of the femoral neck, and the proximal aspect of the femur. The uptake of fluorine in each area was converted to standard uptake volumes. Results: No areas of osteonecrosis were seen in the femoral head of any patient. There were no significant differences in the standard uptake volumes as measured in the four regions of the nonresurfaced hips, whereas the median values were higher in all four regions of the resurfaced hips. The difference between the values in the resurfaced hips compared with those in the nonresurfaced hips was only significant (p < 0.05) in the lateral aspect of the femoral head. Conclusions: This study establishes positron emission tomography in conjunction with injection of fluorine as a possible modality for the assessment of femoral head viability after hip resurfacing. Viability following successful Birmingham hip resurfacing performed through a modified anterolateral approach has also been demonstrated. The increase in bone activity that was seen in the resurfaced hips in our study group may be related to bone remodeling or reperfusion of small areas of osteonecrosis. This technique offers the potential to study femoral head perfusion and viability following all types of resurfacing. Level of Evidence: Diagnostic Level IV. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.