A nacelle for housing a fan within a gas turbine engine having a longitudinal centre line includes a leading edge and a trailing edge. A nacelle length (Lnac) is defined as an axial distance between the leading edge and the trailing edge. An azimuthal angle (θ) is defined about the longitudinal centre line. The nacelle length (Lnac) varies azimuthally. The nacelle length (Lnac) decreases azimuthally from an inboard end of the nacelle to an outboard end of the nacelle.