Paenemarmota Hibbard and Schultz, 1948 includes 3 species of giant ground squirrels within Marmotini (Rodentia, Sciuridae) from the Late Miocene and Pliocene of central and western North America. We developed skeletal and dental models for estimating body mass across modern species of Marmotini and apply these models to Paenemarmota. The most reliable models for estimating body mass of modern species (on the basis of length and width of femur, lengths of p4 and P4) generally yielded lower estimates of body mass for Paenemarmota than less reliable models (on the basis of lengths of m1, m2, M1, and M2). Models that were most reliable across modern species yielded 2 nonoverlapping estimates for P. barbouri Hibbard and Schultz, 1948: 9.5–9.8 kg on the basis of femur dimensions, and 14.4–16.2 kg on the basis of lengths of premolars. On the basis of lengths of premolars, P. mexicana (Wilson 1949) closely resembled P. barbouri in estimated mass (14.4–15.7 kg), but P. sawrockensis (Hibbard 1964) was smaller (10.0–12.4 kg). These large ground squirrels probably differed in mass-dependent biological attributes from all modern marmotines.