Introduction:Neuropathological data and nuclear medicine imaging show extensive serotonergic impairment in Parkinson's disease (PD) and atypical parkinsonian syndromes (APS). The study aims at performing a case-controlled region-of-interest (ROI)-based analysis of 123I–N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl) nortropane (123I-FP-CIT) images to measure extrastriatal regional deficits in PD and APS, and assess their added diagnostic value in discriminating degenerative parkinsonisms from other conditions. Methods: We included 157 patients with early degenerative parkinsonism (mean age 72.6 years, 44% female, mean disease duration at scan 1.6 years), i.e. PD (n = 59), multiple system atrophy parkinsonian variant (MSA-P, n = 17), progressive supranuclear palsy (PSP, n = 28), corticobasal syndrome (CBS, n = 19), dementia with Lewy bodies (DLB, n = 34) as well as 58 similarly-aged control participants. 123I-FP-CIT SPECT images were processed with statistical parametric mapping 12 (SPM12)-based PETPVE12 software and subjected to partial volume effect correction for ROI-based group comparisons. Results: Relative to controls, all forms of degenerative parkinsonism showed decreased 123I-FP-CIT uptake in caudate nucleus, putamen but also pallidum and insula. In addition, a significant uptake reduction was observed in thalamus for MSA-P and PSP, in midbrain for PD and PSP, and in the amygdala for PSP (ANCOVA controlling for age, sex and antidepressant medication, all Bonferroni-corrected p < 0.007). Receiver-operating characteristics area-under-the-curve showed that adding extrastriatal evaluation led to higher accuracies in separating degenerative conditions from control participants (96.1% vs 94.9% with striatal ROIs only, p = 0.045). Conclusion: This study provides evidence of a major extrastriatal 123I-FP-CIT impairment, and therefore of an altered serotonergic transmission in PD and APS, confirming previous neuropathological and SERT imaging findings.