The importance of calcium and phosphorus for the health of reptiles is well known. Proper calcium intake is critical for the prevention of nutritional diseases such as nutritional secondary hyperparathyroidism (NSHP); however, the role magnesium may play in this disease is unknown. Magnesium is the second most abundant intracellular cation in the body and has influence on the function of vitamin D and parathyroid hormone. Chelonians are one of the most common companion reptile groups presenting for NSHP. The purpose of this study was to establish reference intervals for complete blood counts, total calcium, total magnesium, and phosphorus. Peripheral blood was collected in November in the northern hemisphere on a single day from 40 captive red-footed tortoises (Chelonoidis carbonaria). Hematologic and biochemistry assessment included packed cell volume, a blood smear for white blood cell slide estimate and differential count, and plasma concentrations of total calcium, total magnesium, and phosphorus. There was no correlation between total calcium and total magnesium. This population of red-footed tortoises appeared to be predominantly lymphocytic in the season in which samples were collected, and may have also had an absolute basophilia. This is the first study to determine reference intervals for complete blood counts and select biochemistry parameters of a uniform cohort of red-footed tortoises. These values may aid in clinical management and monitoring of red-footed tortoises presenting for veterinary care.