Adrenal incidentalomas detected during pregnancy are very rare, and the natural history of these tumors during gestation is unknown. We report a case of a pregnant woman with an adrenal mass discovered serendipitously, who was followed-up during gestation and underwent adrenalectomy shortly after delivery. This allowed the evaluation of both the clinical outcome and the molecular/immunohistochemical correlates. Estrogens may indeed influence the function and proliferation of human adrenal cells, and a state of circulating estrogen excess can represent an in vivo model to test their effect on the adrenals. No evidence of adrenal change in morphology and function was found in our patient throughout pregnancy, as shown by adrenal ultrasound imaging and adrenal hormone measurements. Four months after delivery, the patient underwent laparoscopic right adrenalectomy, and pathologic analysis revealed a 2.7 cm benign adrenocortical adenoma. The diameter of the adrenal mass at ultrasonography correlated highly with post-partum mass diameter measured by abdominal computed tomography (CT). Quantitative expression of both ERalpha and ERbeta by real-time RT-PCR analysis and Western blotting findings did not differ among adenoma, normal adjacent adrenal and normal adrenal control tissues. This case of an adrenal incidentaloma discovered during pregnancy shows that a close observation with endocrine investigations and ultrasonography could be an appropriate approach, delaying the decision of surgical intervention after delivery. Estrogen receptor mRNA levels in the adrenal mass similar to those observed in normal adrenals suggest that estrogen oversecretion during pregnancy was not a risk factor for tumor progression.