Introduction: Recent literature has suggested an association between short-term exposures to air pollution and sudden cardiac death (SCD). There is little known on the relationship between medium- and long-term exposure to particulate matter air pollution (PM) and SCD. Moreover, most studies focus on PM less than 2.5μm in diameter (PM 2.5 ) and have not considered larger coarse particles (PM 2.5-10 ) or the effect of combined exposures. Methods: 117,358 women in the Nurses’ Health Study, a nationwide prospective cohort, returned biannual questionnaires to update health status and risk factors. Suspected and definite SCD cases from 1988 to 2013 were identified by medical records and next of kin reports. Spatiotemporal models estimated the monthly exposures to PM at each residence. We calculated time-varying 12 month moving averages as a measure of long-term exposure and the difference between 12- and 3-month moving average and the difference between 3-month and 1-month moving averages as measures of medium-term exposure for both PM 2.5 and PM 2.5-10 . Time-varying Cox proportional hazard models were used to examine the association between all size fractions and time windows and SCD, and to calculate hazard ratios with corresponding 95% confidence intervals. The basic model was adjusted for age, year, season, and region, and a full model also considered demographics, medication use, health history, and socioeconomic status. Results: During 2,070,408 person-years of follow-up, there were total 351 definite and probable SCDs. Medium term exposures to both PM 2.5 and PM 2.5-10 were associated with risk of SCD, although the specific time windows of greatest risk varied ( Table 1 ). Notably, in our full model, exposure to PM 2.5-10 was associated with SCD (Hazard Ratio: 1.07; 95% Confidence Interval: 1.02, 1.13). Conclusions: PM air pollution in the past month or season may be an important contributor to the population level risk of SCD.