Dermatitis resulting in mortality of seahorses has been attributed to a number of etiologies including fungi (e.g. Exophiala sp.), protozoa (especially by microsporidian parasites such as Glugea sp.) and bacteria. Seahorses are very sensitive to many of the conventional treatments used in fish, and little information regarding safe and efficacious therapies is available. This report describes two outbreaks of severe necrotizing dermatitis in seahorses maintained at Mystic Marine Life Aquarium and details the successful treatment used in one of the outbreaks. The first outbreak affected 32, adult Ceylon seahorses (Hippocampus fuscus) and the second occurred in 36, five-month-old lined seahorses (Hippocampus erectus). Multiple irregular, focally extensive to coalescing areas of epidermal ulceration with exposure of the underlying white dermis were present on the head, trunk, tail and fins of affected animals from both outbreaks. Whole mount preparations demonstrated large numbers of mixed filamentous and non-filamentous bacteria and lesser numbers of ciliated protozoa. Histopathological findings were consistent with a primarily filamentous bacterial necrotizing dermatitis with secondary protozoal and nematodal involvement. Treatments of the Ceylon seahorses with nitrofurazone, oxytetracycline and chloroquine were unsuccessful and all the members of that collection died. Lined seahorses were treated with a combination of formalin and povidone-iodine (Betadine). Water changes of 50% followed by the addition of formalin at a ratio of 1:60,000 parts tank water was performed every 3 days. A 10% povidone-iodine solution was applied to affected skin every second day. All seahorses continued to eat throughout the 1 to 4 week course of therapy. Animals that no longer appeared to be grossly affected were transferred from the treatment tank to a holding tank. Lesions recurred in five animals within three days after being placed in the holding tank, but resolved after the treatment was resumed. Lesions were evident on 90% of the lined seahorses over the course of the outbreak but 90% of animals that were treated with the povidone-iodine solution and formalin regime recovered completely. This treatment, though non-specific, represents an effective protocol for seahorses with bacterial dermatitis.