Hiccup loses his leg during the final battle with the Red Death in the first How to Train Your Dragon movie.

Quick Scoop: What happened to Hiccup’s leg?

In the climax, Hiccup and Toothless dive in to defeat the giant dragon, the Red Death, causing a huge mid‑air explosion and firestorm. Toothless pulls Hiccup out of the blast and shields him with his body, but Hiccup is badly injured in the process and later wakes up back on Berk to find that the lower half of his left leg is gone and replaced with a prosthetic Gobber built for him.

The exact in‑universe medical detail of how the leg was lost (burned off, crushed, or damaged then amputated) is never explicitly shown or explained on screen. Fans and official wiki notes point out two leading interpretations: either Toothless accidentally injured Hiccup’s leg while grabbing him to pull him from the flames, or the leg was severely burned by the Red Death’s inferno and had to be removed afterward.

So, in short: Hiccup lost his leg as the cost of defeating the Red Death and surviving that final explosion, and it becomes a key part of his character and his mirrored bond with Toothless and his missing tail fin.

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