To assess the type and load of helminths in wastewater and the quality of treatment, we examined the raw and treated wastewater of 8 wastewater treatment plants (WTP) in Tehran and 2 in Isfahan for the presence of helminth eggs during 2002–2003. Wastewater samples obtained from both inlet and effluent of each treatment plant were examined on several occasions using the modified Bailenger method. Untreated entry wastewater in Tehran WTPs contained a larger variety of helminth eggs than those of Isfahan, as well as higher total egg counts. The helminths identified in the influent of Tehran included Ascaris lumbricoides, hookworms, Enterobius vermicularis, Trichostrongylus spp., Taenia spp., Hymenolepis nana and Dicrocoelium dendriticum, while in Isfahan only A. lumbricoides, Trichostriogylus and H. nana were isolated. After treatment, the number of eggs/L fell to  1 egg/L.