A 37-year-old man who had fathered a child five years previously presented with erectile and ejaculatory disorder. Endocrinological examinations revealed isolated luteinizing hormone-releasing hormone (LHRH) deficiency of hypothalamus, resulting in hypogonadotropic hypogonadism, and no causative abnormality was detected in imaging studies, including magnetic resonance imaging (MRI). Having a diagnosis of adult-onset hypogonadotropic hypogonadism, the patient received pulsatile subcutaneous administration of gonadotropin-releasing hormone (GnRH). Sperm analysis and serum level of testosterone improved to normal in a few months. His wife became pregnant using artificial insemination with her husband's semen 15 months after the beginning of the treatment.