The health of 44 wild ring-tailed lemurs (Lemur catta) at the Bezà Mahafaly Special Reserve was assessed across three age classes: <5 yr (young), 5–9 yr (adult), and ≥10 yr (old). Hematology and biochemistry tests were performed manually (leukocyte count and differential, packed cell volume, total protein) and using a point-of-care analyzer (hematocrit, hemoglobin, glucose, blood urea nitrogen, creatinine, sodium, potassium, chloride, ionized calcium, total carbon dioxide, anion gap), respectively. Urine specific gravity was measured via refractometry. Age- and sex-related differences were detected. Old lemurs had significantly lower lymphocyte count than adult and young lemurs, leading to markedly lower total leukocyte count and higher neutrophil-to-lymphocyte ratio. Decreased lymphocyte count with advanced age is consistent with immunosenescence. Young lemurs had significantly higher total protein, monocyte count, and potassium than adult and old lemurs but significantly lower ionized calcium than adult lemurs. Males had significantly higher leukocyte, neutrophil, and monocyte counts; lower percentage basophils; and higher blood urea nitrogen than females. Females had markedly higher glucose than males. Young females had the highest monocyte count and total protein, which were significantly lower in the adult and old age classes. Basophil count was stable in females across age but dropped precipitously in males in the adult and old age classes. Within adult and old age classes, males had significantly higher blood urea nitrogen and lower basophils than females. Glucose was significantly higher after α2 agonist administration. Identifying age-related hematologic and biochemical changes in apparently healthy wild ring-tailed lemurs will aid in clinical diagnosis and treatment of lemurs in human care, which is especially relevant for management of geriatric animals in zoo populations. Equally important, a better understanding of the ability of aging lemurs to tolerate environmental stressors will inform the capacity for this species to cope with ongoing and future habitat alteration.