OBJECTIVE This study investigated the effect of in vitro accelerated aging reproduced with thermocycling on the bond strength of three commercially available permanent denture soft liners (PermaSoft, Dentuflex, Ufi-gel) with one heat-polymerized polymethyl methacrylate resin denture base (QC-20) by tensile test. METHODS Ten specimens were prepared for control and test groups of each material for a total of 60 specimens. All controls were stored in water (37 degrees C) for 24 hours before testing. All test groups received 3000 thermal cycles consisting of 1 minute at 5 degrees C and 1 minute at 65 degrees C. All specimens were submitted to a tensile test using a universal testing machine at a crosshead speed of 5 mm/min. Results were statistically analyzed (ANOVA, p < or = 0.05, Tukey's post-hoc test). RESULTS The mean bond strength of control specimens was (MPa): 0.32 (Ufi-gel), 0.49 (PermaSoft), and 1.19 (Dentuflex). There was no statistical difference (p > 0.05) between Ufi-gel and PermaSoft, but both were statistically different (p < 0.05) when compared to Dentuflex. After thermocycling, the mean bond strength was (MPa): 0.18 (Ufi-gel), 0.81 (PermaSoft), and 3.32 (Dentuflex). All materials were statistically different (p < 0.05). Ufi-gel had the lowest value and Dentuflex the highest in both control and test groups. Dentuflex presented only adhesive failure; in the remaining groups, there was no predominant failure mode, except Ufi-gel control with no adhesive failure. CONCLUSIONS Despite presenting greater bond strength, thermocycling had a deleterious effect in Dentuflex; Ufi-gel may be adequate for short-term use.