Context: Adrenocortical carcinomas are uncommon, and their evaluation by [18F]fluorodeoxyglucose positron emission tomography (FDG PET) has not been well evaluated. Objective: The purpose of this study was to examine the potential utility of FDG PET in the detection of recurrent or metastatic adrenocortical carcinoma. Design: In patients with known adrenocortical carcinoma who underwent FDG-PET imaging for suspected recurrence or metastasis, FDG activity was compared with other imaging findings, clinical features, and the presence or absence of disease as confirmed by resection, biopsy, or clinical follow-up. Setting: The study took place at four tertiary referral centers. Patients or Other Participants: Twelve patients (10 females and two males, 5-71 yr of age) were evaluated. Main Outcome Measures: The main outcome measures were FDG activity, other imaging findings, and clinical features. Results: Abnormal FDG uptake correctly indicated tumor recurrence in 10 patients. One patient with no abnormal FDG activity had a morphological abnormality subsequently proven to be a postoperative scar. Two patients, one with very small pulmonary lesions and one with a hepatic metastasis, had false-negative findings. Conclusions: Most adrenocortical carcinomas accumulate and retain FDG and thus can be visualized by PET. However, false-negative findings are possible, especially with very small lesions.