Background Sex differences in heart diseases, including acute coronary syndrome, congestive heart failure, and atrial fibrillation, have been studied extensively. However, data are lacking regarding sex differences in pericarditis and myopericarditis patients. Objectives The purpose of the study was to evaluate whether there are sex differences in pericarditis and myopericarditis patients as well. Methods We performed a retrospective, single-center observational study that included 200 consecutive patients hospitalized with idiopathic pericarditis or myopericarditis from January 2012 to April 2014. Patients were evaluated for sex differences in prevalence, clinical presentation, laboratory variables, and outcome. We excluded patients with a known cause for pericarditis. Results Among 200 consecutive patients, 55 (27%) were female. Compared with men, women were significantly older (60 ± 19 years vs 46 ± 19 years, P < .001) and had a higher rate of chronic medical conditions. Myopericarditis was significantly more common among men (51% vs 25%, P = .001). Accordingly, men had significantly higher levels of peak troponin (6.8 ± 17 ng/mL vs 0.9 ± 2.6 ng/mL, P < .001), whereas women presented more frequently with pericardial effusion (68% vs 45%, P = .006). Interestingly, women had a significantly lower rate of hospitalization in the cardiology department (42% vs 63%, P = .015). Overall, there were no significant differences in ejection fraction, type of treatment, complications, or in-hospital mortality. Conclusions Most patients admitted with acute idiopathic pericarditis are male. In addition, men have a higher prevalence of myocardial involvement. Significant sex differences exist in laboratory variables and in hospital management; however, the outcome is similar and favorable in both sexes.