Hematology and serum chemistry evaluations are essential to a patients comprehensive health exam by providing measures of organ function, blood cell volume and health status. Reference ranges have to be established to interpret that the values are within normal limits. Presently, hematology and serum chemistry results from healthy, sick and injured Hawaiian monk seals are interpreted using past studies, which were limited by small samples sizes across age classes, collected from captive Hawaiian monk seals or established using frozen samples. This study builds on previous studies in sample size, quality and demographic representation to establish blood reference ranges by using samples collected between 2004 and 2015 from wild monk seals of multiple age classes (n=65 seals; 28 adults, 18 subadults, 8 juveniles, 11 weaned pups). Samples were analyzed by a single veterinary diagnostic laboratory within 24 hours of collection from apparently healthy, free-ranging wild seals sampled opportunistically during population monitoring and research activities. Reference ranges were developed for 50 complete blood cell counts and serum chemistry parameters using the mean of the values within two standard deviations. While there are several possible approaches to establishment of reference ranges, this method was chosen to maintain consistency with those used by the veterinary diagnostic laboratory most commonly used for sample analysis. Key indices evaluated include total white blood cell count (WBC; mean- 8.145 K/uL, SD-1.73 ), red blood cell count (RBC; mean- 3.397 M/uL, SD- 0.46), hematocrit (mean- 51.56%, SD- 4.99), and total serum protein (TP; mean- 7.625g/dL, SD- 0.81). The development of comprehensive hematology and serum chemistry reference ranges for Hawaiian monk seals will enable more consistent and systematic interpretation of results, which will aid in the assessment and treatment of seals in rehabilitation and the determination of health status of seals sampled during translocation and other research/recovery activities.