This study reports the evaluation of the hearing results after implantation of a Teflon piston of a different diameter in cases of otosclerosis. Randomly 34 times a 0.3 mm and 26 times a 0.4 mm shaft diameter Teflon piston was inserted. A retrospective analysis of the pre- & post-surgery audiological results of these two patient groups was carried out by microcomputer. A statistical repeated measures analysis of variance was used to test and estimated the air-conduction frequency specific differences between the two prostheses with respect to the change in post-operative and pre- operative hearing loss. We demonstrated a difference in hearing results between two pistons with different shaft diameter by measuring more frequencies (especially the low frequencies) than performed in the other studies. We believe that it is important to measure more frequencies for the evaluation of the hearing results of stapes surgery. The results of this comparative study of two Teflon pistons with a different diameter indicate statistically a bigger hearing gap for the 0.4 mm prosthesis especially in the lower frequencies. It is doubtful that the optimal prosthesis has been developed and that all patients should have the same piston implanted in cases of otosclerosis. More comparative studies are needed to support the statements of this present study