1. The breeding success of the pukeko or swamphen, Porphyrio porphyrio melanotus, was studied for three seasons in two different habitats in the Manawatu, New Zealand. 2. There was a direct relationship between clutch size and the number of birds in a territory. In groups the dominant female was at a reproductive advantage, laying more eggs overall, but especially in the first and more successful clutch. Dominant females in groups were still at a disadvantage compared with females breeding in a pair. 3. Overall reproductive success was greater for pairs than for groups, although much of this difference could be attributed to habitat variables and membership stability. 4. Attempts to measure the ‘helping effect’ of non-reproductive helpers were inconclusive. The advantages and disadvantages to individuals are discussed, and it is concluded that breeding success is of limited value in explaining the communal habit of pukeko.