Annual health records were retrospectively analyzed for a colony of ring-tailed lemurs (Lemur catta) inhabiting St. Catherines Island, Georgia, USA to establish baseline hematological and serum biochemical parameters and determine sex- and age-related differences. Summarized complete blood count and serum biochemistry panel results are presented for 85 blood samples collected from 54 lemurs at annual health exams during 1998–2003. Within each of four age classes (infant, <1 yr; juvenile, 1–5 yr; adult, ≥ 6 yr), data were stratified and summarized based on sex. Lemur age was a significant positive predictor of mean corpuscular hemoglobin; absolute concentrations of neutrophils, monocytes, and band cells; serum concentrations of blood urea nitrogen (BUN), creatinine, globulins, lipase, and total protein; and gamma-glutamyl transferase (GGT) activity. Lemur age was a significant negative predictor of albumin:globulins ratio; alkaline phosphatase (ALP) activity; and serum concentrations of calcium, cholesterol, glucose, magnesium, phosphorus, potassium, and triglycerides. Neutrophil proportions increased with aging and lymphocyte proportions decreased with aging, particularly in females. Recent steep population declines of wild ring-tailed lemurs make their successful husbandry and medical care an increasingly pressing concern. These biomedical data will aid in clinical diagnosis and treatment of lemurs in human care, and support conservation efforts for this species.