We report the case of a man with idiopathic lymphocytic orchitis (LO) manifested by undifferentiated testicular pain and atrophy. Conventional investigation results were unremarkable. Oral ciprofloxacin only improved the pain temporarily. Scrotal exploration surgery was performed to exclude acute testicular torsion and a biopsy was taken during surgery for histological examination. Histology revealed severe LO with reduced spermatogenesis. A trial of oral steroids was initially effective but the effect was temporary. Due to chronic pain, he eventually underwent unilateral orchidectomy. Histology confirmed the initial diagnosis of LO. He was pain-free postoperatively. Idiopathic LO is a rarely reported cause of testicular atrophy.