Few studies have investigated the independent health effects of different size fractions of particulate matter (PM) in multiple locations, especially in Europe. We estimated the short-term effects of PM with aerodynamic diameter = 10 µm (PM10), = 2.5 µm (PM2.5), and between 2.5 and 10 µm (PM2.5–10) on all-cause, cardiovascular, and respiratory mortality in 10 European Mediterranean metropolitan areas within the MEDPARTICLES project. We analyzed data from each city using Poisson regression models, and combined cityspecific estimates to derive overall effect estimates. We evaluated the sensitivity of our estimates to co-pollutant exposures and city-specific model choice, and investigated effect modification by age, sex, and season. We applied distributed lag and threshold models to investigate temporal patterns of associations. A 10-µg/m3 increase in PM2.5 was associated with a 0.55% (95% CI: 0.27, 0.84%) increase in all-cause mortality (0–1 day cumulative lag), and a 1.91% increase (95% CI: 0.71, 3.12%) in respiratory mortality (0–5 day lag). In general, associations were stronger for cardiovascular and respiratory mortality than all-cause mortality, during warm versus cold months, and among those = 75 versus < 75 years of age. Associations with PM2.5–10 were positive but not statistically significant in most analyses, whereas associations with PM10 seemed to be driven by PM2.5. We found evidence of adverse effects of PM2.5 on mortality outcomes in the European Mediterranean region. Associations with PM2.5–10 were positive but smaller in magnitude. Associations were stronger for respiratory mortality when cumulative exposures were lagged over 0–5 days, and were modified by season and age.