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Population sizes and distribution of waders in New Zealand were determined for the first time during summer and winter, 1983-1994. In winter (June/early July), 163 000 New Zealand breeding and 21 000 Arctic migrant waders were recorded, and in summer (November/early December) 37 000 New Zealand breeding and 166 000 Arctic migrant waders were recorded. Species accounts, including seasonal totals for each year 1983-1994, average counts at favoured sites, and distribution maps are presented for the most abundant New Zealand breeding and Arctic migrant waders. The pied oystercatcher Haematopus ostralegus was the most abundant New Zealand breeding wader; the estimated winter total of over 112 000 birds showed that the population had increased by about 128% since 1970-71. Counts of pied stilt Himantopus himantopus (estimated winter total c. 28 000 birds) and banded dotterel Charadrius bicinctus (c. 11 000 birds) provided the first population estimates for these species during winter in New Zealand. However, both are significantly underestimated because many overwinter inland in sites not counted. Also, most of the banded dotterel population migrates to Australia following the breeding season. Wrybill Anarhynchus frontalis (c. 3900 birds) was next most abundant native species counted in winter, with most birds recorded in the North Island. Counts of spur-winged plover Vanellus miles, variable oystercatcher Haematopus unicolor, New Zealand dotterel Charadrius obscurus, black-fronted dotterel Charadrius melanops, and black stilt H. novaezelandiae also substantially underestimated population sizes because most birds of these species do not use estuarine sites during winter. During summer, bar-tailed godwit Limosa lapponica, lesser knot Calidris canutus, and turnstone Arenaria interpres were the most abundant of the Northern Hemisphere migrants with estimated populations of c. 102 000, 59 000 and 5100 birds, respectively, representing significant proportions of the East Asian-Australasian flyway populations of these species. Less than 700 birds were recorded during summer for each of the other Northern Hemisphere migrants, including (in decreasing order of abundance) Pacific golden plover Pluvialis fulva, red-necked stint Calidris ruficollis, whimbrel Numenius phaeopus, curlew sandpiper C. ferruginea, sharp-tailed sandpiper C. acuminata, and eastern curlew N. madagascariensis. Counts of uncommon Arctic migrants (i.e. those which reach New Zealand in most years) are also given.