Abstract: 18F-DOPA PET/CT but not 68Ga-DOTA-TOC PET/CT revealed the cause of ectopic Cushing syndrome in a 61-year-old man. The patient presented with rapid weight gain, swollen legs, and sleep disturbances. Plasma potassium level was 2.7 mM (reference range, 3.3–4.9 mM), 24-hour urinary cortisol level was 13,124 nmol (reference range, 30–144 nmol), and plasma adrenocorticotropin level was 61 ng/L (reference range, <48 g/L). CT demonstrated prominent lymph nodes in the left lung hilus and hyperplastic adrenals but no primary tumor. 68Ga-DOTA-TOC PET/CT, which is recommended as the first-line PET imaging, was performed, but it was not diagnostic. Imaging with 18F-DOPA PET/CT revealed the underlying cause.