We made accelerometric recordings of the tremor induced by valproic acid. The tremor was similar to essential tremor and appeared within a month of starting therapy. It was present at rest and exacerbated by action or antigravity positioning. There was no close correlation of tremor severity and plasma valproate level, but the tremor usually appeared at dosages greater than 750 mg per day. This tremor has appeared in 20 of 25 patients recently studied. In some patients the tremor is markedly active; however, others note only minimal tremor activity.