Background: Greyhound dogs have numerous clinicopathologic differences compared with other dog breeds, most notably in their hematologic profiles. The hematologic differences are likely related to breed; however, the influence of other factors, including age, sex, and training, has not been fully determined. Objectives: The aim of this study was to assess hematologic values in young, healthy, pretraining Greyhounds and to determine the effects of age and sex on these findings. Methods: Jugular venous EDTA-anticoagulated blood samples were collected from 43 healthy, pretraining Greyhounds between 5 and 13 months of age. Samples were analyzed within 24 hours of collection on an Abbott CELL-DYN 3500R hematology analyzer. Mean hematologic results for different age groups, and correlation with age and sex were determined for each analyte. Results were compared with adult canine, nonbreed-specific reference intervals. Results: From the age of 9 to 10 months, Greyhounds had higher HCT, hemoglobin concentration, and RBC counts compared with adult canine reference intervals. Younger Greyhounds (5–6 months) had values comparable with reference intervals. Mean total WBC, neutrophil, lymphocyte, and platelet counts tended to be toward the lower end or below the reference intervals. HCT, hemoglobin concentration, and RBC counts were correlated positively with age, and platelet count was correlated negatively with age. No differences were found based on sex. Conclusions: These results confirm that significant hematologic differences exist in pretraining Greyhounds by 9 to 10 months of age, when compared with adult canine, nonbreed-specific reference intervals; however, these differences are less marked in Greyhounds 5 to 6 months old. Given these findings, it is unlikely that factors such as training or racing are responsible for differences in hematologic values between adult Greyhounds and other breeds.