Objective. We set out to determine the ability of positron emission tomography with fluorodeoxyglucose to detect groin lymph node metastases from vulvar cancer. Methods. From January 2000 to August 2001, patients with squamous cell cancer of the vulva undergoing radical excision and lymphadenectomy were offered preoperative positron emission tomography. The imaging and pathologic status of each patient and groin were compared, and the sensitivity, specificity, and predictive value of positron emission tomography in predicting nodal metastasis were determined. Results. Fifteen patients underwent positron emission tomography prior to exploration of 29 groins. Six patients had positive scans, suggesting metastases in 8 groins. Pathologically, 5 patients had metastases in 9 groins, with positron emission tomography demonstrating metastases in 4 of 5 patients and 6 of 9 groins with disease. On a patient-by-patients basis, positron emission tomography had a sensitivity of 80%, specificity of 90%, positive predictive value of 80%, and negative predictive value of 90% in demonstrating metastases. On a groin-by-groin basis, positron emission tomography had a sensitivity of 67%, specificity of 95%, positive predictive value of 86%, and negative predictive value of 86%. Positron emission tomography was more accurate in detecting extranodal metastases than disease confined within the groin nodes (P = 0.048). Conclusions. Positron emission tomography is relatively insensitive in predicting lymph node metastasis, and a negative study is not a reliable surrogate for a pathologically negative groin. However, the high specificity suggests that positron emission tomography is useful in planning radiation therapy and as an adjunct to lymphatic mapping and sentinel lymph node dissection.