Background Primary hyperaldosteronism may be caused by an aldosterone-producing adenoma (APA), which is correctable by unilateral adrenalectomy or by idiopathic adrenal hyperplasia, a bilateral disease without any indication for surgery. This study sought to assess the prevalence and the results of surgery in unilateral adrenal hyperplasia (UAH). Methods The study included 35 patients who underwent unilateral adrenalectomy because of primary hyperaldosteronism after unequivocal successful lateralization by adrenal venous sampling. Demographics, biochemical evaluation, and blood pressure were assessed pre- and postoperatively. Pathology was categorized as APA (isolated adenoma), nodular (multiple micromacronodules), and diffuse UAH (gland thickening without nodules). Results Pathology revealed 9 APAs and 23 nodular and 3 diffuse UAHs. Patients with APAs and UAHs were statistically similar regarding demographics and preoperative blood pressure levels. Bilateral adrenal involvement was evident at imaging in 10 patients (11% in APA versus 35% in UAH, P = NS). After surgery, biochemical cure of the disease was achieved in all patients; blood pressure levels normalized in 66.6% of patients and ameliorated in 22.2% in APA versus 34.6% and 50% in patients with UAH (P = NS). At a long-term follow-up, only 1 patient with nodular UAH experienced a biochemical recurrence of disease. Conclusion UAH is not rare, sharing the same features of APA. When disease lateralization is confirmed by adrenal venous sampling, unilateral adrenalectomy achieves excellent long-term results.