Before driving provisional conclusions from available studies directly addressing Th17 and IL-17 in PD patients and in animal models of the disease, a few additional indirect lines of evidence about Th17/IL-17 and PD deserve consideration to put the issue in full context, namely: (i) the correlation between PD and immune-related disease, (ii) recent studies about gut microbiome in PD and (iii) on vitamin D, and (iv) emerging evidence regarding dopaminergic modulation of Th17 cells and (v) the influence of Th17 on glial cells. The gene discussed is IL17A; the disease is Parkinson disease.