Purpose: Blood cells play a major role in homeostasis and inflammation. Primary dysmenorrhea (PD) involves the production of prostaglandins and leukotrienes, which cause inflammation in uterine tissue. Aim of this study was to investigate whether there is a relation between complete blood count parameters and PD during the menstrual cycle. Materials and Methods: The study included 41 cases diagnosed as primary dysmenorrhea (mean age, 23.02 +/- 3.43 years) and 40 individuals who control subject (mean age, 23.76 +/- 3.13 years). Hematologic parameters were measured on menstrual phase (day 1-4), follicular phase (day 9-12), and luteal phase (day 21-23) during menstrual cycle. Results: There were no statistically differences between hematological parameters of two groups except for mean platelet volume (MPV). MPV of PD and control groups at each phase of menstrual cycle were 7.71 vs 8.61 (p = 0.01); 7.66 vs 8.56 (p = 0.005); 7.75 vs 8.53 (p = 0.01), respectively. Conclusion: PD is associated with decreased MPV and platelets may be involved in the inflammatory process of PD.