Surgery to separate conjoined twins is taking place today in Phoenix.

Alex and Angel Mendoza were born in mid-August. They are joined from just below their sternums all the way down through their pelvises.

Click here to see photos of a pair of conjoined twins that were successfully separated.

Doctors say the boys are healthy for the most part. Much of the work in the operation will center on their livers, plus the pelvis area. The boys each have one liver, but they are fused together.

Today's surgery will include more than 20 doctors and nurses, and is expected to last 12 to 18 hours.

The babies were delivered two months early after doctors saw there was not enough amniotic fluid supporting them.