The aim of this study was to assess whether adolescent cases of periodontitis present with different hemogram findings than control subjects. This case-control study comprised 87 adolescent cases presenting with clinical attachment loss ≥3 mm in at least two teeth and 73 control subjects. Blood samples were obtained by venipuncture and analyzed in an Abbott Cell-Dyn 3,500 hematology analyzer for values of white blood cells and red blood cells, hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, red-cell distribution width, platelets, and mean platelet volume. Hematocrit values were obtained using volume fractions read from capillary tubes. The associations between log-transformed hemogram variables with each of the three exposure variables "case status" (yes/no), a "high percent sites with PD ≥4 mm" (yes/no), and a "high percent sites with BOP" (yes/no) were investigated using multivariate linear regression analyses. Periodontitis cases presented with 5% higher values for the mean platelet volume than did controls. Subjects with a high percent sites with probing depth ≥4 mm had eosinophil counts that were on average 27% lower than among subjects with fewer deepened pockets. They also had 7% higher values for the mean platelet volume than did persons with less pocketing. Eosinophil counts and mean platelet volumes may be associated with the parameters of periodontitis in adolescents. While standard hematological testing did not show abnormalities in adolescents with periodontitis compared to healthy controls, eosinophil counts and mean platelet volumes may reflect periodontal inflammation.