An improved delay-dependent H_∞ filtering design is proposed for linear, continuous, time-invariant systems with time delay. The resulting filter is of the Luenberger observer type and it guarantees that the H_∞ norm of the system, relating the exogenous signals to the estimation error, is less than a prescribed level. The filter is based on the application of the descriptor model transformation and Park’s inequality for the bounding of cross terms. The advantage of the new filtering scheme is clearly demonstrated via simple examples.