<p>East Pacific green turtles (<i>Chelonia mydas</i>) inhabit tropical and subtropical waters along the western coast of the Americas. This population uses the Gulf of California, Mexico, as a primary area for feeding and refuge, where they face various stressors. This study aimed to establish hematological reference intervals for healthy green turtles in this area (<i>n</i> = 326), as well as evaluate seasonal variations in blood parameters and compare values between healthy turtles and individuals affected by fibropapillomatosis (<i>n</i> = 25). Reference intervals for hematological analytes were estimated following the American Society for Veterinary Clinical Pathology guidelines. Seasons significantly influenced hemoglobin, hematocrit and heterophils, which were lower during the cold season, while monocytes and eosinophils were significantly higher. These variations were attributed to physiological effects of cooler water temperatures, shorter photoperiods, reduced food intake, and immune response to seasonal stressors during the colder months. Turtles with visible fibropapillomatosis tumors were mildly affected, with tumor sizes not exceeding 5-cm diameter (tumor score 1). While significant alterations were observed in some hematological analytes (i.e., lower hemoglobin and hematocrit, and higher WBC, lymphocytes and heterophil: lymphocyte ratio), these values remained within the reference intervals estimated for healthy turtles. Additionally, no abnormalities commonly associated with severe fibropapillomatosis were observed, suggesting minimal structural or functional damage at tumor score 1 stage. This baseline information will help evaluate intra-population trends, assess potential impacts from future ecosystem changes, and develop effective conservation strategies for this threatened population.</p>