one of my outdoor pond's goldfish has badly distended sides.  at first i thought it was a female with eggs, but it has been this way far too long.
any ideas as to what this is and whether i need to do anything?
thanx!

Could be lots of things!

Is the whole fish bloated? And if so, are the scales standing out? That would be dropsy, and you need to treat the fish with oral antibiotics ASAP!

If it's only parts of the body that are swollen, it could either be internal tumors or possibly some internal parasites/worms in the body cavity. For this, I would treat with medicated food against parasites/worms

But like Hanna said, it'd be good if you'd post a pic! And I would also want you to test your water's pH, ammonia, nitrite and nitrate levels!!