A popular species in the pet trade, and therefore in the illegal wildlife trade, the diamond-backed terrapin, Malaclemys terrapin terrapin, population has seen significant declines. Associated with the illegal wildlife trade, occasions arise in which terrapins are confiscated, and no standard operating procedures exist for repatriation into the wild. To develop such procedures, an understanding of the pathogens circulating in the wild diamond-backed terrapin population in New Jersey is needed. We sampled 30 wild female diamond-backed terrapins for herpesvirus, Mycoplasmopsis, ranavirus, and intestinal and blood parasites and performed white blood cell counts and differentials and evaluated biochemistry values. Terrapins had an average age of 10 yr (8–15 yr), and 70% were gravid at the time of sampling. Thirty-three percent of the sampled northern diamond-backed terrapins were positive for Mycoplasmopsis sp., and all were negative for ranavirus and herpesviruses. Occasional blood parasites were found, and few intestinal parasites were noted. There was no significant difference between gravid status and any of the blood parameters (P<0.05). Blood chemistry values appeared to vary according to feeding activity; no differences were noted in the values in relation to gravid status. Four terrapins had heterophil to lymphocyte (H:L) ratios above 4.5, significantly higher than the other terrapins sampled, which may indicate inflammation. Two of the four had Mycoplasmopsis, one sample was contaminated by other bacteria and was discarded, and one was negative. No significant difference was found between Mycoplasmopsis infection status and H:L ratio (P=0.926). Our findings, though conducted on a small number of female terrapins at a specific time point, provide data on the pathogens that may be circulating in this population, adding to the current body of knowledge and helping to guide decision making for the reintroduction of confiscated diamond-backed terrapins into New Jersey's wild population.