The helminth parasites of the gastro-intestinal tract of the Paradise Shelduck Tadorna variegata (Gmelin) are surveyed together with aspects of the shelduck's ecology (particularly food and feeding habits). Twenty-two species of helminth parasite (19 from the gastro-intestinal tract), including one new species of notocotylid, are recorded from 281 shelducks examined. Their normal locations are noted. The new species is described and an account of its life history is given. The life history of a second notocotylid species, Uniserialis gippyensis, is described for the first time and the New Zealand intermediate host of a cosmopolitan cestode, Cloacotaenia megalops, is identified. Present knowledge of the life histories of all other helminth species found in the Paradise Shelduck is reviewed, and probable New Zealand intermediate hosts are suggested. Quantitative aspects of the helminth infections are examined, and comparisons made between burdens of adult and juvenile hosts, and males and females. Seasonal fluctuations in levels of infection are discussed. For comparison with the shelducks, helminth fauna and food of "dabbling ducks" and geese from the study area are investigated. The host-parasite-environmental interrelationships are discussed in an attempt to explain the composition and dynamics of the shelduck's helminth fauna. A brief discussion of pathology is included.