Objective To study the effects of gender and age on occurrence of myocarditis.

Design Nationwide, multicentre registry study in Finland.

Setting All medical hospital admissions (n=1 698 397) of patients aged ≥16 years during 9.5 years in 29 hospitals.

Patients 3198 myocarditis patients.

Results Myocarditis was more common in men (76.61%; 95% CI 75.11% to 78.05%) than in women (23.39%; 95% CI 21.95% to 24.89%, p<0.0001). Median age of patients was 33 years (IQR 23–50 years). Male patients were significantly younger than females (mean age 34.1±SD 15.1 vs 49.0±18.7 years, p<0.0001). In men, occurrence was highest at 16–20 yrs of age, with a linear decline to elderliness (r=−0.95, p<0.0001). By contrast, myocarditis affected women more evenly at all ages with highest occurrence at the age of 56–60 years. Myocarditis caused 0.19% (95% CI 0.18% to 0.19%) of all medical admissions, and 0.48% (95% CI 0.46% to 0.49%) of admissions due to cardiovascular reasons with an inverse logarithmic association with age (r=−0.97, p<0.0001). Admissions were more commonly caused by myocarditis in men (risk ratio 3.11; 95% CI 2.87 to 3.38, p<0.0001).

Conclusions Men are significantly more susceptible to myocarditis than women. Young men are especially at risk for acquiring myocarditis, while women are affected most commonly at the postmenopausal age. The proportion of hospital admissions caused by myocarditis has an inverse, logarithmic association with age.