The obturation of highly curved canals often poses a problem for the clinician using lateral condensation. Recently, a product that incorporates guttapercha with a carrier (Thermafil) has been marketed. This study asked, "Was there a difference in apical microleakage of highly curved canals obturated with the Thermafil versus lateral condensation?" Twenty-two extracted human molars with canal curvature greater than 30 degrees were instrumented using a step-back technique. Teeth were placed in two groups of 10 teeth. Two teeth were controls. Canals were either obturated using sealer and lateral condensation, or sealer and the Thermafil technique. The access was closed with Cavit. Teeth were coated with wax and placed into India ink for 48 h. The wax was removed and teeth were cleared. All teeth were evaluated for linear dye penetration using a x7 viewer. A t test resulted in t = 0.137 (p > 0.05). Mean leakage for teeth obturated with the Thermafil was 1.15 mm and was 1.09 mm for lateral condensation. The Thermafil technique resulted in similar dye penetration to lateral condensation in highly curved canals.