Since the first description of Down syndrome, imitation has been a reputed strength of persons with trisomy 21. The question is: How many elementary movements can persons with trisomy 21 imitate simultaneously and successively? As a baseline, we developed elementary movements that are easy to imitate separately. They are combined such that there are no recognizable repetitions or other regular patterns. In all of the 713 test subjects there was a limit to the number of correctly imitated elementary movements. Whereas neurotypical subjects reached their limit by imitating four elementary movements, persons with trisomy 21 could imitate only two elementary movements. Diagnostic and learning methods currently need to be reassessed, because they do not consider these special imitation limits.