Open biopsy of the corpus cavernosum was performed in 13 nondiabetic patients with erectile dysfunction. The history and physical examination, sleep rigidity and tumescence monitoring, hormonal assays, duplex ultrasonography with papaverine, and cavernosometry and cavernosography, formed the basis of categorizing each patient into 1 of 5 etiological groups. These groups included neurogenic, moderate arterial, severe arterial, venous and fibrotic causes for organic erectile dysfunction. The cavernous smooth muscle and endothelium in each patient appeared to be normal on light and electron microscopy. We conclude that cavernous biopsy is of limited value to determine therapeutic options in patients with erectile dysfunction.