We investigated the abundance of the tegu lizard (Tupinambis merianae) in a 21 787 ha Brazilian Atlantic forest fragment (Reserva Natural Vale, RNV). This remnant has a highly irregular perimeter and an extensive network (126 km) of internal unpaved roads. We hypothesized that the high proportion of these edge habitats might benefit active heliothermic lizards like tegus due to greater incidence of sunlight. We estimated population density using the program DISTANCE, and compared sighting frequency of tegus along twelve 500 m long transects located at three distances (25, 200 and 400 m) from the nearest unpaved road or fragment edge. We found no significant differences in sighting frequency among the three distances (Chi-square; chi(2) = 4.308; P = 0.116) and no significant association between edge distance and edge type (internal, external) (G test adjusted; G(2) = 0.617; P = 0.734). However, as the test comparing distances had relatively low power we assumed that the experimental evidence was not strong enough to prove lack of an edge effect. The estimated density (0.63 +/- 0.13 lizard/ha) is within the range of densities found on Brazilian islands where tegus have proliferated to the point of becoming a threat to ground nesting birds and turtles. We caution, however, that the absence of published data on other non-island sites prevents us from concluding that the species has an abnormally high density in RNV.