text: sometimes when i ejaculate, no sperm comes out, can someone tell me why>?   there are several different things that can cause your problem. retrograde ejaculation, undescended testicles, or blocked or missing ducts. if you have a retorgrade ejactulation your bladder isn't closing correctly, so all the sperm goes backwards. i'm sure you would already know if you have undescended testicles, and that one is pretty straight forward. blocked or missing ducts would cause a low sperm count.