Our rationale was to conduct a retrospective study comparing 3 I--ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane (I-FP-CIT) SPECT quantitative methods in patients with neurodegenerative syndromes as referenced to neuropathologic findings. I-FP-CIT-SPECT and neuropathologic findings among patients with neurodegenerative syndromes from the Mayo Alzheimer Disease Research Center and Mayo Clinic Study of Aging were examined. Three I-FP-CIT SPECT quantitative assessment methods-MIMneuro, DaTQUANT, and manual region-of-interest creation on a workstation-were compared with neuropathologic findings describing the presence or absence of Lewy body disease (LBD). Striatum-to-background ratios (SBRs) generated by DaTQUANT were compared with the calculated SBRs of the manual method and MIMneuro. The left and right SBRs for caudate, putamen, and striatum were evaluated with the manual method. For DaTQUANT and MIMneuro, the left, right, total, and average SBRs and scores for whole striatum, caudate, putamen, anterior putamen, and posterior putamen were calculated. The cohort included 24 patients (20 [83%] male, mean age for all patients at death, 75.4 ± 10.0 y). The antemortem clinical diagnoses were Alzheimer disease dementia ( = 6), probable dementia with Lewy bodies ( = 12), mixed Alzheimer disease dementia and probable dementia with Lewy bodies ( = 1), Parkinson disease with mild cognitive impairment ( = 2), corticobasal syndrome ( = 1), idiopathic rapid-eye-movement sleep behavior disorder ( = 1), and behavioral-variant frontotemporal dementia ( = 1). Seventeen (71%) had LBD. All 3 I-FP-CIT SPECT quantitative methods had an area under the receiver-operating-characteristics curve ranging from more than 0.93 to up to 1.000 ( < 0.001) and showed excellent discrimination between LBD and non-LBD patients in each region assessed ( < 0.001). There was no significant difference between the accuracy of the regions in discriminating the 2 groups, with good discrimination for both caudate and putamen. All 3 I-FP-CIT SPECT quantitative methods showed excellent discrimination between LBD and non-LBD patients in each region assessed, using both SBRs and scores.