Life-history details of the live-bearing Peripatoides novaezealandiae (Hutton) were obtained by measuring and dissecting field collected animals. As in other studies, the sexes were found to have different demographics. Sex-specific weight frequency distributions and regression of weight vs length suggest sex differences in patterns of growth and/or mortality. Mature males were smaller than mature females; females apparently undergo a further period of growth between maturity and the onset of embryo production. The sex ratio of the whole sample was female biased; the sex ratio in the smallest size class was 1:1, and then oscillated from female- to male-, and then back to female-biased as size increased. Embryos were unable to be sexed. The sex ratios in individuals of mature (i.e. mating) size, and of reproductive size, were both 1:1. Females, especially but not exclusively before the onset of embryo production, had widely varying numbers of sperm in their haemolymph, indicating dermal-haemocoelic sperm transfer. These data also suggest that females are able to mate throughout life. Numbers of sperm in spermathecae of females were negatively correlated with body size. Fecundity increased with size in both sexes, somewhat more so in females. Embryo weight was correlated with maternal weight only at the beginning of the embryo's development. Rotting logs containing small populations contained a disproportionate number of large females.