We assessed the effect of radiotelemetry on the growth, reproduction, and survival of black ratsnakes (Elaphe obsoleta) using data from a 6-year study. Transmitters were surgically implanted for more than one year and were <2.5% of the snakes' mass and 3.8% of their length. Compared to snakes without transmitters, snakes with transmitters exhibited lower annual growth in mass but not length, and females produced lighter clutches of eggs relative to their body size. Although results were equivocal, radiotelemetry also may have adversely affected survival. Potential explanations for the negative effects of radiotelemetry include direct effects of transmitters on snakes (impaired behavior, cost of transportation, infection) and indirect effects (increased disturbance by researchers). Because we conducted the study at the northern limit of the species' distribution, snakes in this population may be particularly sensitive to the negative effects of radiotelemetry. Despite the apparent costs, we believe that use of radiotelemetry is still warranted because of the benefits realized.