This study explored the possible association between dermatomyositis or polymyositis (DM or PM) and the subsequent risk of herpes zoster (HZ). We used data from the Taiwan National Health Insurance (NHI) system to address the research topic. The exposure cohort comprised 2023 patients with new diagnoses of DM or PM. Each patient was frequency matched according to age, sex, index year, and comorbidities including diabetes, renal disease, obesity, malignancy, rheumatoid arthritis, immunodeficiency virus infection, autoimmune disease not elsewhere classified, mixed connective tissue disease, or vasculitis with 4 participants from the general population who did not have a history of HZ (control cohort). Cox proportional hazards regression analysis was conducted to estimate the relationship between DM or PM and the risk of subsequent HZ. The incidence of HZ in the exposure and control cohorts was 35.8 and 7.01 per 1000 person-years, respectively. The exposure cohort had a significantly higher overall risk of subsequent HZ than did the control cohort (adjusted hazard ratio [HR] = 3.90, 95% confidence interval [CI] = 3.18-4.77). The risk of HZ in patients with DM or PM in whichever stratification (including sex, age, and comorbidity) was also higher than that of the control cohort. The findings from this population-based retrospective cohort study suggest that DM or PM is associated with an increased risk of subsequent HZ. A synergistic effect was observed between DM or PM and one of the comorbidities.