To investigate the types of intestinal parasites that infected people living in Islamic period southern Iberia (al-Andalus), and compare with other regions of Europe.Four cesspits from 10th-11th century CE Córdoba (Spain), and two from 12th-13th century Mértola (Portugal).Sediment from each cesspit was analyzed using digital light microscopy and enzyme-linked immunosorbent assay (ELISA).Analysis revealed eggs of roundworm (Ascaris lumbricoides) in every cesspit analyzed, but no evidence of other species of helminth or protozoal parasites.Differences were noted between parasite species found in Mediterranean Europe and northern Europe, where a range of zoonotic parasites were endemic alongside sanitation-related parasites. We suggest that the scarcity of zoonotic parasites in southern Europe in the medieval period may reflect contrasts in climate between northern and southern Europe.The repeated identification of roundworm eggs suggests that al-Andalus was less hygienic than historically depicted. We did not note a difference between parasites found in Muslim and Christian regions of Iberia, and the predominance of parasites spread by fecal contamination of food is consistent with past research.The eggs of some species of parasite are fragile, so may theoretically have been present in the population but did not survive for us to identify them.To further investigate the role of climate upon the parasites that affected past human populations.