Cushing's syndrome and pheochromocytomas (PCCs) are associated with endocrine hypertension. Cortisol-producing adrenal adenomas are a major cause of Cushing's syndrome. Simultaneous occurrence of cortisol-producing adrenal adenomas and PCCs is rare. Additionally, a PCC generally produces catecholamines in proportion to its size; therefore, micro-PCCs are rarely found in clinical practice. It is unknown whether micro-PCCs produce excess catecholamines during the pre-biochemical phase. Herein, we report the case of a 53-year-old woman who was referred to our hospital for further evaluation of left adrenal incidentaloma. She had been suffering from hypertension for 7 years. Endocrine tests indicated autonomous cortisol secretion, and she was diagnosed with cortisol-producing adrenal adenoma. A laparoscopic left adrenalectomy was performed. The final pathological examination revealed an adrenocortical adenoma measuring 26 × 24 mm. In addition, a micro-PCC measuring 3 × 2 mm was incidentally found near the cortisol-secreting adrenal adenoma in the ipsilateral adrenal gland. All catecholamine biosynthetic enzymes, tyrosine hydroxylase, aromatic l-amino acid decarboxylase, dopamine β-hydroxylase, and phenyl ethanolamine N-methyltransferase, were detected in this micro-PCC by immunohistochemical analyses. Although catecholamine levels were not biochemically elevated, the PCC expressed catecholamine biosynthetic enzymes. This is the first immunohistochemical report to show that a micro-PCC produces excess catecholamines in the pre-biochemical phase.