Müllerian refers to the Müllerian ducts, also called paramesonephric ducts. They are paired embryonic structures that develop into much of the internal female reproductive tract.

In a typical female fetus, the ducts form:

In a typical male fetus, fetal testicular Sertoli cells produce anti-Müllerian hormone (AMH), which causes these ducts to regress. Failure of this process can cause persistent Müllerian duct syndrome, where uterine or fallopian-tube tissue remains in an otherwise male individual.

Problems in their formation, fusion, or canalization can cause Müllerian anomalies, such as a septate uterus, bicornuate uterus, or absent/underdeveloped uterus and upper vagina. NCBI embryology overview and Medical Physiology describe their female derivatives as the fallopian tubes, uterus, and upper third of the vagina.