OBJECTIVE: To evaluate whether visual assessment of [I-123]-FP-CIT (DaTSCAN(TM), Nycomed Amersham, pie) single photon emission computerized tomography (SPECT) images can differentiate between parkinsonism and essential tremor (ET). METHODS: [I-123]-FP-CIT SPECT imaging was conducted in a six-center study of 158 patients with a clinical diagnosis of parkinsonism compared with 27 ET cases and 35 healthy volunteers. Striatal uptake of the radioligand was graded normal or abnormal, and abnormal images were further graded to three levels of severity. An institutional read whereby each center visually assessed the images blinded to the clinical data and a consensus blinded read by a panel of five was undertaken. RESULTS: The institutional reading scored 154 of 158 cases of parkinsonism abnormal, all 27 cases of ET as normal, and 34 of 35 healthy volunteers as normal compared with the consensus blinded read scoring 150 cases of parkinsonism as abnormal, 25 ET cases as normal, and 33 healthy volunteers as normal. Sensitivity for the clinical diagnosis of parkinsonism was 97% and specificity for ET was 100% for the institutional read, whereas sensitivity was 95% and specificity 93% for the consensus blinded read. Semiquantitative analysis of specific: nonspecific caudate and putamen uptake were consistent with the results of visual inspection. CONCLUSION: Visual assessment of [I-123]-FP-CIT SPECT images is an easily applied diagnostic test which is helpful in the differential diagnosis of tremor disorders and in confirming a clinical diagnosis of a hypokinetic-rigid syndrome.