THE INFLUENCE OF THE FRECUENCY CONTENT OF SEISMIC EXCITATIONS ON THE BEHAVIOR OF AN OPTIMAL TUNED MASS DAMPER (TMD) IS STUDIED IN THE CONTEXT OF A SYSTEM WITH EXPLICIT CONSIDERATION OF SOIL-STRUCTURE INTERACTION. A STOCHASTIC ANALYSIS IS MADE IN THE TIME DOMAIN FOR TWO RANDOM PROCESSES, ONE CONSIDERING A BROAD BANDWIDTH PROCESS (BBP) AND OTHER CONSIDERING A NARROW BANDWIDTH PROCESS (NBP). A STRUCTURE BUILT OVER THREE DIFFERENT TYPES OF SOIL (SOFT, MEDIUM AND HARD) IS CONSIDERED. FOR THE OPTIMIZATION OF THE TMD, THE MINIMIZATION OF THE RATIO BETWEEN THE STANDARD DEVIATION OF THE DISPLACEMENT OF THE MAIN STRUCTURE WITH TMD WITH RESPECT TO A STRUCTURE WITHOUT TMD, IS USED AS THE TARGET FUNCTION. IT IS FOUND THAT FOR SEISMIC EXCITATIONS WITH HIGH FRECUENCY CONTENT, THE RATIO OF THE TMD FREQUENCIES COMPARED TO THE FIXED BASE FREQUENCY OF THE STRUCTURE APPROACHES TO 1 AS THE SOIL BECOMES MORE RIGID. IT IS ALSO OBSERVED THAT THE TMD BECOME TUNED WITH THE FLEXIBLE BASE FREQUENCY FOR ALL SOIL TYPES, PRODUCING PERFECT TUNING FOR SMALL MASS RATIOS AND DETUNING GRADUALLY FOR HIGHER MASS RATIOS. ON THE OTHER HAND, THE TMD OPTIMAL DAMPING RATIO INCREASES AS THE TMD MASS RATIO IS HIGHER, INDEPENDENTLY OF THE SOIL TYPE. THE TMD IS MORE EFFICIENT FOR HIGHER VALUES OF THE TMD MASS RATIOS, ESPECIALLY ON SOFT SOIL.