Diagnostic imaging of tumor manifestations in persistent medullary thyroid carcinoma (MTC) is difficult and diagnostic sensitivity and specificity of the available methods is unsatisfactory. Exact localization of any residual tumor by means of diagnostic imaging would be of great importance for a successful reoperation. We report the treatment, diagnostic procedures and the clinical course over 5 years in a 45-year-old woman with persistent sporadic medullary thyroid carcinoma. Calcitonin levels were still elevated after three surgical interventions and diagnostic imaging failed to detect tumor tissue. By means of positron emission tomography with ¹⁸F-DOPA mediastinal lymph node metastases were localized for the first time preoperatively and allowed subsequent surgical removal of one of these tumor manifestations. This case demonstrates that imaging with ¹⁸F-DOPA-PET may be a valuable tool supplementing other methods of diagnostic imaging to depict lymph node metastases in medullary thyroid carcinoma.