The ecological requirements of brown bears are poorly known in the Himalaya region, which complicates conservation efforts.  We documented the diet of the Himalayan brown bear ( Ursus arctos   isabellinus ) by combining classical scat analysis and a newly developed molecular genetic technique (the  trn L approach), in Deosai National Park, Pakistan. Brown bears consumed over 50 plant species, invertebrates, ungulates, and several rodents.  Eight plant families; Poaceae, Polygonaceae, Cyperaceae, Apiaceae, Asteraceae, Caryophyllaceae, Lamiaceae, and Rubiaceae were commonly eaten with graminoids comprising the bulk of the diet.  Golden marmots comprised the major mammalian biomass in the park, and were also the main meat source for bears.  Animal matter, making 36% of dietary content, contributed half of the digestible energy, due to its higher nutritious value.  We did not find a significant temporal pattern in diet, perhaps because the availability of the major diet (graminoids) did not change over the foraging period.  Male brown bears were more carnivorous than females, probably because of their larger size, which requires higher energy and also makes them more efficient in capturing marmots.  Frequencies of three plant species were also significantly higher in male brown bears;  Bistorta affinis ,  Carex diluta , and  Carex  sp.  Diet of the brown bear differed significantly between the park and surrounding valleys.  In valleys, diet consisted predominantly of graminoids and crops, whereas the park provided more nutritious and diverse food.   The estimated digestible energy available to brown bears in Deosai was the lowest documented among brown bear populations, due to the lack of fruits and a relatively lower meat content.  The low nutritious diet and high cost of metabolism in a high altitude environment, probably explains the very low reproductive potential of this population