Although you already have extremely long hair, I'd highly recommend you read through the suggestions in the long hair guide on this site.  http://www.longlocks.com/how-to-grow-long-hair.htm

To try to detangle what you currently have, I would try using a LOT of conditioner or oil, then try to detangle from the ends while the hair is wet (as in the shower or tub).  Be very gentle with the hair, as it is vulnerable to stretching and breaking when wet.  Use a hair pick or wide toothed detangling comb, preferrably one that does not have rough edges or seams on it.

Trimming any split or broken ends will also help as these frequently are the cause of tangles as they grab other hairs.

A task as yours will be difficult and enlisting help from friends or family may be necessary.

Good Luck!

Well, just to keep Anne-Marie from sounding like a commercial  I'll add that I, too, use Matrix Biolage Conditioning Balm, as does my hairdresser. (I bought it on Anne-Marie's suggestion and then discovered that said hairdresser, who has long hair, uses it, too.)

Great stuff. Between using that and wearing my hair in a braid as often as possible, I'm getting a lot fewer tangles. And, what's more, my hair is actually starting to look and feel like hair again, as opposed to a straw-like mess.

My hair is *nowhere* near your length. But, maybe if you can get it untangled once and then keep it a) super-well-conditioned and b) braided or otherwise not flopping, you can avoid future woes.

You might find more ideas under my own personal plea for help, "Fine, dry hair in the desert."

Good luck. And, ankle-length hair - wow!!

Christine