A laminar flow nacelle for an aircraft engine (10) has an outer member (26) defining an aerodynamic shape. The nacelle (24) has an inner member (28) defining a chamber (30) with the outer member (26) of the nacelle (24). The outer member (26) of the nacelle (24) has a porous region (32) at a first region (34) of the outer member (26) and the porous region (32) allows a flow of fluid into the chamber (30). A duct (36) connects the chamber (30) to an aperture (38) in the outer member (26) at a second region (40) of the outer member (26) downstream of the first region (34). In operation the static pressure at the first region (34) is greater than the static pressure at the second region (40) such that the boundary layer of the fluid flows through the porous region (32) at the first region (34) through the duct (36) to the aperture (38) at the second region (40). The first region (34) extends between 10% and 20% of the chord length of the nacelle (24) from the highlight (42) of the nacelle (24). The second region (40) extends between 50% and 70% of the chord length of the nacelle (24) from the highlight (42).