Ticks, Aponomma sphenodonti, were collected from tuatara, Sphenodon punctatus, in the field and also obtained from a captive host in the laboratory. Developmental times of life history stages were determined, both at a constant 18°C and at ambient temperatures that ranged from 10 to 26°C. Feeding times and longevity of freeliving stages were also determined. The duration of the life cycle allowed for one generation annually or two every 3 years, depending on whether minimum or maximum developmental times were considered. Although copulation was only observed to occur off the host, it is just as likely to occur on the host because of the substantial numbers of attached males. Additional data from collections of preserved ticks permitted an estimate of the seasonal activity of each active tick stage. All stages were common around the time of host nest building, although there is no clear evidence to suggest that the tick is nidiculous, and larvae were most numerous long before the host's eggs were laid. Aponomma sphenodonti appears to be capable of tolerating a lower host temperature than is the case for at least one other species of reptile tick in the genus. This report is the first record of biological data for Ap. sphenodonti.