We report behavioural findings implying common motion processing for auditory and visual motion. We presented brief translational motion stimuli drifting leftwards or rightwards in the visual or auditory modality at various speeds. Observers made a speed discrimination on each trial, comparing current speed against mean speed (i.e., method of single stimuli). Data were compiled into psychometric functions and means and slopes compared. Slopes between auditory and visual motion were identical, consistent with a common noise source, although mean speed for audition was veridical while visual speeds were significantly underestimated. An inter-trial analysis revealed clear motion priming in both audition and vision (i.e., faster perceived speed after a fast preceding speed, and vice versa – a positive serial dependence). Plotting priming as a function of preceding speed revealed the same slope for each modality. We also tested whether motion priming was modality specific. Whether vision preceded audition, or audition preceded vision, a positive serial bias (i.e., priming) was always observed. We conclude a common process underlies auditory and visual motion, and that this explains the closely matched data in vision and audition, as well as the crossmodal data showing equivalent motion priming regardless of the preceding trial’s modality.