We estimated effective population size (N_e) in Collared Lizards (Crotaphytus collaris) via ecological and genetic methods. The ecological method employed life-history data from three years of mark-recapture studies and yielded an N_e estimate of 46. The genetic method used allele frequency changes over one generation and yielded an N_e estimate of 33 (95% CI; 10, 76). Dispersal, measured as displacement of territories or home ranges in one season, was low (average = 30.5 m) and did not differ among life-history stages or between sexes. Gene flow among habitat patches at our study site appeared sufficient to prevent genetic divergence or subdivision within the population. The observed small effective population size supports models of evolution in C. collaris, wherein stochastic processes could influence strongly the evolution of this species. Similarities in estimates of N_e suggest that the effective population size of this population does not differ from the size of a recent founder population and, moreover, that genetic and ecological methods yield compatible results when assumptions of the two methods are satisfied by the study design.