Recent vibration problems with floors used for aerobics have shown the need for better guidelines for structural design and evaluation. Such guidelines were introduced for the first time in the Supplement to the 1985 National Building Code (NBC), but more recent experience with one particular floor has shown the need for some improvements to these guidelines. The paper describes the investigation of the floor and the use of the floor to estimate the loading function for aerobics, and recommends changes to the NBC design criteria. The paper provides guidance on estimating parameters used in the criteria and discusses repair alternatives related to the floor problem.Key words: floor vibration, aerobics, design criteria, repair.