I have a couple of double sideds. They don't work at all on my portable induction. It doesn't recognize them. They do heat up on my Gaggenau, but don't work the way one would like.

Your best bet is a flat, round griddle. Lodge makes them. So do others. Maybe not vintage, but gorgeous can be had.

I meant to mention--Induction makers warn against the ridge thing. Hot air can build up underneath and burn you when you move it, and there are some rumors (I haven't been able to find credible confirmation, but it sounds possible) that this can also damage the cooktop.

Above the surface works. It's the continuous ridge that's a potential problem.

Unless you have zoneless, a round griddle will heat more evenly.

eugenie11: "My question: can you use a cast iron double griddle on induction? I'm looking at some vintage Lodge and Griswold on eBay and they're gorgeous, but they all seem to have a ridge around the edge that raises the griddle surface off the cooktop and my understanding of induction is that the pan and hob have to be in contact."

A two-part answer: on the bridged elements of our LG LCE30845 induction cooktop, the LG-included steel oblong griddle works fine. But the second part of the answer is more important to your question.

The second part is that a vintage Griswold cast iron 11" round griddle that we use on the 11" burner was cast with an outer circumferential rim that holds the underside of the main part of the griddle less than one millimeter above the Ceran cooktop surface, so the griddle touches the cooktop only around the rim. That one works very well on our cooktop, also.