Crossing dispersal barriers with hostile environments is difficult for species with low environmental tolerance. Thus low environmental tolerance could result in small geographic ranges. In the case of mainland biotas, where mountain ranges are important dispersal barriers, this means species range size would decrease with the species inability to tolerate high altitude conditions. This idea predicts endemic species are more sensitive to elevational barriers than non-endemic species, other things being equal. Here, I test this prediction in the Mediterranean herpetofauna (southern Europe), using reported maximum altitude as a surrogate for tolerance to altitude. After correcting for sampling effects (influence of range size on reported altitude), phylogeny, and topographic biases (regional availability of maximum altitudes), a strong pattern is revealed: endemic amphibians and reptiles reach lower maximum altitudes than nonendemic counterparts. This suggests range size is controlled by the species ability to cross elevational barriers. Available data suggest this may be a general trend among endemics from mainland biotas.