Dear Editor,rnFour patients with erectile dysfunction (ED) induced by pituitary prolactinoma presented to our clinic from 2007 to 2008.The patients had been misdiagnosed nearly 2 years earlier at other hospitals because severe ED was the initial symptom.None of these patients had experienced successful and satisfactory intercourse in approximately 2 years despite being treated with numerous medications,including the repeated administration of phosphodiesterase-5 inhibitors (PDE5is)(sildenafil 100 mg and/or tadalafil 20 mg).However,after successful treatment for pituitary prolactinoma,the response to PDE5is improved dramatically.The four cases are described in this report.