Tlstá (meaning fat in Slovak) is a mountain in the Bralná Fatra part of the Greater Fatra Range, measuring . It is located over the Turiec Valley, rising steeply nearly above the valley bottom. It has rugged slopes with many rock spires and rock terraces under the grass-covered summit. With its well-preserved forests, rare plants and many karst caves in the massif, the mountain and its surrounding area were declared a National Nature Reserve in 1981, covering an area of . Together with the opposite Ostrá Mountain and Gader Valley beneath them, they create one of the most valuable and picturesque parts of the Greater Fatra Range.