This study examines whether global tempo and expressive timing microstructure are independent in the aesthetic judgment of music performance. Measurements of tone interonset intervals in pianists' performances of pieces by Schumann ("Traumerei") and Debussy ("La fille aux cheveux de lin") at three different tempi show a tendency toward reduced relative variation in expressive timing at both faster and slower tempi, relative to the pianist's original tempo. However, this could reflect merely the pianists' discomfort when playing at an unfamiliar tempo. Therefore, a perceptual approach was taken here. Experimental stimuli were created artificially by independently manipulating global tempo (three levels) and "relative modulation depth" of expressive timing (RMD, five levels) in MIDI-recorded complete performances of the Schumann and Debussy pieces. Skilled pianists rated the quality of the resulting two sets of 15 performances on a 10-point scale. The question was whether the same RMD would receive the highest rating at all three tempi, or whether an interaction would emerge, such that different RMDs are preferred at different tempi. A small but significant interaction was obtained for both pieces, indicating that the listeners preferred a reduced RMD when the tempo was increased, but the same or a larger RMD when the tempo was decreased. Thus, they associated an increase in tempo with a decrease in (relative) expressive timing variation, which, in general agreement with the performance data, suggests that the two temporal dimensions are not independent.