We extend the classical Carathéodory extension theorem to quasiconformal Jordan domains ( Y , d Y ). We say that a metric space ( Y , d Y ) is a quasiconformal Jordan domain if the completion ̄ Y of ( Y , d Y ) has finite Hausdorff 2-measure, the boundary ∂ Y = ̄ Y \ Y is homeomorphic to 𝕊 1 , and there exists a homeomorphism ϕ : 𝔻 →( Y , d Y ) that is quasiconformal in the geometric sense. We show that ϕ has a continuous, monotone, and surjective extension Φ: 𝔻 ̄ → Y ̄. This result is best possible in this generality. In addition, we find a necessary and sufficient condition for Φ to be a quasiconformal homeomorphism. We provide sufficient conditions for the restriction of Φ to 𝕊 1 being a quasisymmetry and to ∂Y being bi-Lipschitz equivalent to a quasicircle in the plane.