Hiccup loses his helmet when Snotlout throws a rock at it thus knocking it off his head, revealing his Slavemark. Hiccup leaves the helmet behind during the dragon attack at Flashburn's School of Swordfighting. Fishlegs puts on the helmet after Hiccup escapes as a way to remind himself and Camicazi of Hiccup's bravery. What happened to the helmet after that is unknown as when Fishlegs is seen again in Book 10 he lacks the helmet.
During the between How to Steal a Dragon's Sword and How to Seize a Dragon's Jewel, Hiccup stole a new helmet to keep undercover. However Hiccup wasn't fond of the helmet as it was too big and uncomfortable.
Hiccup lost this helmet as well when Snotlout was pretending to be him so he could escape. Alvin the Treacherous and Excellinor the Witch obtain the helmet, and show it to the Dragonmarkers as proof that Hiccup is dead, though in reality Hiccup survived, because Snotlout was pretending to be Hiccup so he could escape.