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The Persian Long-tailed Desert Lizard, Mesalina watsonana , is one of the most common and most widely distributed lizards on the Iranian Plateau extending from Iran to Pakistan and Afghanistan. The species is frequently encountered in various types of habitats. We collected over 600 distributional records from available literature, museum collections, and our own field work and used bioclimatic and land cover characteristics to develop a model of potential distribution for M. watsonana . According to the model, the most important factors limiting the distribution of M. watsonana are: precipitation in wettest quarter exceeding 250–300 mm, precipitation in coldest quarter lower than 40 mm and exceeding 250 mm, altitudes above 2500 m and slopes steeper than 10.5°. The model suggests that most of the Iranian Plateau is suitable for the species except for some isolated areas such as the Dasht-e Kavir and Dasht-e Lut deserts in Iran, Helmand basin in Afghanistan, the Karakum Desert in Turkmenistan, the western Chagai-Kharan deserts of Pakistani Balochistan, and Thar and Cholistan deserts in eastern Pakistan. The most important factor in these regions appears to be the extremely low rainfall during coldest quarter of the year. The outer boundary of the distribution of M. watsonana follows important biogeographic barriers that are also clearly delimited by climatic conditions.