Nematodes of the family Mermithidae were found parasitizing adults and larvae of the sharpshooter species Hortensia similis (Walker, 1851). The host specimens were collected from weeds associated with citrus orchards located in Corrientes state, Argentina during a biodiversity study in 2015. This first example of a mermithid parasitism of leafhoppers is as far as we know the first record for South America.