Although sensory symptoms were not originally described in Parkinson's disease (PD), in recent years it has been increasingly recognized that painful sensations and paresthesias occur in approximately 40% of patients. It has been our observation that PD patients often describe a sensation of internal tremor, a feeling of tremor inside the chest, abdomen, arms, or legs that cannot be seen. We investigated the prevalence and characteristics of internal tremor by administering a questionnaire to 100 consecutive patients with PD and 50 age-matched controls seen in our movement disorders center. A sensation of internal tremor was present in 44% of this sample of PD patients and in 6% of the control population (p < 0.0001). The presence of internal tremor was unrelated to Unified Parkinson's Disease Rating Scale score, Hoehn and Yahr stage, duration of disease, or the presence of observable tremor. The frequency of other sensory symptoms (aching, tingling, burning) was higher in the PD patients with internal tremor (73%) than in those without (45%; p = 0.005). Internal tremor is associated with anxiety in 64% of patients (p < 0.0001). It was described as uncomfortable and was unrelieved by antiparkinsonian medication in three quarters of patients. A sensation of internal tremor is commonly reported by PD patients and should be recognized as a useful diagnostic factor in PD.