We explored infection patterns and temporal dynamics of the protozoan blood parasite Hepatozoon tuatarae (Apicomplexa) infecting the tuatara (Sphenodon punctatus), a protected reptile living on Stephens Island, New Zealand. In March 2006, we surveyed tuatara in five study sites to examine spatial variation in infection prevalence, and four times, from May 2005 to November 2006, we recaptured marked individuals within three study sites to examine the temporal dynamics of infection. We also examined how blood-parasite infection patterns were influenced by host sex, body size, and host infestation with ticks (Amblyomma sphenodonti) and mites (Neotrombicula spp.), which are potential vectors of the blood parasite. Infection prevalence (16.9-24% infected) and intensity (<0.01-0.1% blood cells infected) were low in all samples. Infection intensity varied among the five sampled sites in March 2006, but prevalence did not. Neither infection prevalence nor intensity varied with time, and infections were detected in consecutive samples from recaptured individuals for up to 18 mo. Neither survey showed an influence of host sex on infection, but both surveys showed infection intensity declined with increasing host body size, as did infection prevalence in the spatial survey. In the temporal survey, we found a positive relationship between the tick numbers on hosts and blood-parasite infection intensity, which were stronger in two of the sampling periods and among larger hosts. These data suggest that exposure and susceptibility to infection decreases with host size and that ticks, but not mites, are probably the vectors in this ancient host-parasite association of a long-lived (>50 yr) host.