Archaeological sediments can be used to retrieve evidence for parasites that infected past populations, giving evidence for disease, diet, sanitation, and migration in the past. To increase our understanding of parasite infections in Roman Britain and determine which parasites may have infected people living at Vindolanda, sediment samples were collected from a drain connected to a latrine at the bath complex of Vindolanda. These samples were used to look for preserved parasite eggs and cysts deposited in the drain with the faeces of people who used the latrine. Microscopic analysis was used to identify eggs of helminths, and enzyme-linked immunosorbent assay (ELISA) was used to look for protozoan parasites that can cause severe diarrhoea. Eggs of Ascaris sp. (roundworm) and Trichuris sp. (whipworm) were found by microscopy and Giardia duodenalis was detected using ELISA. All of these parasites are transmitted by the faecal-oral route, usually through contaminated food and water. This is the first evidence for G. duodenalis in Roman Britain. A range of zoonotic and faecal-oral parasites have been found at other sites in Roman Britain, yet the drain studied from Vindolanda only contained faecal-oral parasites that can be transmitted directly between humans. This predominance of faecal-oral parasites is similar to a pattern found in large urban sites in the Roman Mediterranean and other military sites in the empire. In contrast, sites from larger urban cities in Roman Britain, such as London and York, appear to have a more diverse range of parasites.