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Breeding of North Island kokako (Callaeas cinerea wilsoni) was studied at Mapara, King Country, New Zealand, from 1990 until 2000. Sixty-seven adult and 167 nestling kokako were colour-banded, and radio-transmitters were attached to 49 to identify individuals and to help locate nests. Pair bonds were stable: 7% of pairs split each year for reasons other than mate death. More than 200 nests were located, which permitted observations of breeding-season length, nesting behaviour, clutch and brood size, incubation and nestling periods, and nest success. The nesting season began in late Oct but varied greatly in duration, lasting from 7 weeks in 1993/94 to 21 weeks in 1994/95. We attributed this variation to changes in abundance of key food fruits. Females made up to 5 breeding attempts and fledged as many as 6 chicks in a season. Male-male pairs also built nests, though the apportioning of effort differed from that of conventional pairs. Mean clutch and brood sizes were 2.31 and 1.96, respectively. The incubation period was 18 days and fledging took a further 34-42 days. Sixty-one percent of nesting attempts successfully fledged young when mammalian pests were controlled, as against 8% when there was no predator control. Predation of eggs and chicks by ship rats (Rattus rattus) and brush-tailed possums (Trichosurus vulpecula) was the main cause of nest failure, whereas deaths of nesting adult females mostly caused be stoats (Mustela erminea). Kokako are well adapted to cope with avian predation, but their future conservation depends on management of key small mammalian pests.