Deep pelvic midline (Müllerian duct) cysts may cause obstruction of the ejaculatory duct. Two previously fertile patients with adult-onset azoospermia and one patient with severe oligozoospermia were each found to have a Müllerian duct cyst. Semen characteristics included low volume and pH, and absent semen coagulation, odor, and fructose. Vasography showed a retroprostatic and/or retrovesical cyst that communicated with the ipsilateral ejaculatory duct, reflux from the cyst into the contralateral ejaculatory duct, and absent communication of the cyst with the urethra. Transurethral incision of the cyst was successful in one patient and unsuccessful in another. Pregnancy was established by the successfully treated patient. Müllerian duct cyst may cause obstructive azoospermia or oligozoospermia, which may be progressive in adult life, and which is compatible with previous fertility.