Guana is a 297-ha island in the British Virgin Islands, a private wildlife sanctuary where human activity is largely restricted to small areas associated with an upscale resort hotel. Guana is free of mongooses and sustains a population of racers (Borikenophis portoricensis; Dipsadidae). Between 2001 and 2012 we marked B. portoricensis with Trovan passive integrated transponders and recorded 394 captures of 367 unique adults (males = 167; females = 200; sex ratio of 0.8 : 1) in an effective trapping area of 25.8 ha. Using contemporary capture-recapture models, we estimated annual adult apparent survival, abundance, and realized population growth. We detected no difference in apparent adult annual survival of males (0.50, 95% confidence interval [CI] = 0.34-0.66) and females (0.50, 95% CI = 0.33-0.66). Recapture probabilities of males (0.09, 95% CI = 0.04-0.18) and females (0.08, 95% CI = 0.04-0.16) were similarly indistinguishable. Annual estimates of adult abundance ranged from 368 to 540, but confidence intervals overlapped broadly between years. We estimated realized population growth as 0.98 (95% CI = 0.75-1.28) over the 12-yr study. Based on the effective trapping area (25.8 ha), average density was 19 adults/ha (range = 14-21 adults/ha). The low recapture probabilities suggest that animals spend much of their lives in areas not accessible to researchers, but we detected little evidence of substantive movement. The population on Guana appears to be healthy, suggesting that declines elsewhere are indeed the results of human activities, especially the introduction of mongooses.