Background: Changes in platelet indices have been reported in patients with panic disorder (PD). However, previous study findings are contradictory and inconclusive. The aim of this study was to evaluate and compare the platelet indices in patients with PD. Materials and Methods: Patients with PD (n = 123) and healthy controls (n = 133) were enrolled in this case control study. The platelet indices (mean platelet volume [MPV] and platelet distribution width [PDW]) along with red blood cell (RBC) indices (RBC count and red cell distribution width [RDW]) were compared between the two groups using the unpaired t-test. Results: Patients with PD had lower MPV (7.53 +/- 0.93 fL vs. 8.91 +/- 1.24 fL, P < 0.0001), higher PDW (16.96 +/- 0.85 fL vs. 14.71 +/- 2.07 fL, P < 0.0001), and higher platelet count (274.2 < 80.66 x 10(9) L-1 vs. 243.1 +/- 93.89 x 10(9) L-1, P < 0.005) than the healthy controls. Furthermore, there were significant differences between patients with PD and healthy controls in terms of their RBC count (4.32 < 0.56 x 10(12) L-1 vs. 4.08 +/- 0.80 x 10(12) L-1, P = 0.007) and RDW (16.48 +/- 2.26 fL vs. 15.01 +/- 2.25 fL, P < 0.0001). Conclusion: Patients with PD have increased PDW and RDW. The platelet and RBC indices may prove to be useful etiological and prognostic markers in patients with PD.