The pathways for migration of phosphorus flame retardants (PFRs) from flame-retardant-treated polyester curtains to indoor dust were investigated. Two possible migration pathways were compared quantitatively: (1) an indirect pathway in which the PFRs in the curtains first evaporate from the curtains and are then adsorbed onto indoor dust and (2) a direct pathway in which the PFRs are directly transferred to dust placed on the curtains. The contribution of the indirect pathway was evaluated by means of emission cell tests, which showed that the area-specific emission rate from a curtain treated with tris(1,3-dichloroisopropyl) phosphate (TDCPP) was 0.17 μg m-2 h-1. The contribution of the direct pathway was evaluated by measurement of the time dependence of PFR concentrations on the indoor dust placed on the curtains. The direct migration rate of TDCPP was 12 μg m-2 h-1. The direct pathway can be expected to predominate.