Mark - My VERY thin ferret, Nicky, was found to have a large mass of hair in his stomach - he was active and otherwise seemed normal. I wonder if yours could have some kind of partial blockage that is keeping him from eating enough. I also have a couple of ferrets who are chronically on the thin side, for no apparent reason - usually they put on a little more weight when winter comes. I believe it's possible that especially long-bodied or "hyper" ferrets may sometimes be harder to keep the weight on. You should have your vet give your ferret a thorough examination to rule out any medical problem. My ferrets with heart disease are also on the thin side. Cherrisa - Please do not wait to have your ferret checked by your vet. Again, the image of a partial blockage comes up, but I would also wonder about intestinal bacterial infection or ulcer. Whenever a ferret is not eating or pooing normally it is most certainly a sign that something is wrong - whether serious or not, that is for your vet to decide and treat accordingly. Joanie Williams and Huggy, Pansy, Daisy, Buddy, Dinky, Fooie, Sparky, Mickey, Rascal, Desiree, Smokey, Cinnamon, Maranda, Parming, Tippy, Frosty, Danci, Pepper, Mischief, Seraphine, Honey, Precious, Thiefa, Silky, Cloe, Natasha, Dusty, Romey, Snowy, Timmy, Tommy, Shammy, Petunia, Nicky, Scotty, and Juneau at Ferret Haven. [Posted in FML issue 1724]