In this study, a fast, simple and efficient ultrasound-assisted emulsification microextraction (USAEME) method was successfully developed based on applying low density organic solvents. Fourteen microliters of toluene was injected slowly into a 12 mL home-designed centrifuge glass vial containing an aqueous sample that was located inside the ultrasonic water bath. The formed emulsion was centrifuged and 2 microL of separated toluene (about 4 microL) was injected into a gas chromatographic system equipped with a flame ionization detector (GC-FID) for analysis. Some polycyclic aromatic hydrocarbons (PAHs) were selected as model compounds for developing the method and evaluating its performance and to compare the efficiency of the proposed method with previously reported techniques. Several factors influencing the emulsification, extraction and collection efficiency such as the nature and volume of organic solvent, emulsification-extraction temperature, ionic strength and equilibrium and centrifugation times were investigated and optimized. Under the optimum conditions, preconcentration factors (PFs) in a range of 1776-2714 were obtained. The performance of the proposed method was studied in terms of linear dynamic range (LDRs from 0.05 to 100 microg L(-1)), linearity (R(2) > or = 0.994), precision (repeatability: RSD% < or = 7.9, reproducibility: RSD% < or = 14.6) and extraction percents (59.2-90.5%). Limits of detection (LODs) in the range of 0.02-0.05 microg L(-1) were obtained for different PAHs. The applicability of the proposed method was evaluated by the extraction and determination of PAHs from several natural water samples.