Seasonality in tourism is a regular and predictable cycle of visitation across a year. Although seasonality in visitation is extremely common and is known, in principle, often to be driven by temporal changes in a range of natural and institutional factors, the relative importance of different individual pressures has yet to be quantified for any large-scale geographical areas. To assess the relative importance of natural versus institutional factors in driving tourism seasonality, data on visitation patterns were collated from 23 protected areas across six Koppen climate zones in eastern Australia. Analyses sought to determine the degree to which climatic variables (such as mean monthly rainfall and minimum and maximum temperatures) explained visitation patterns, and to understand how these relationships could assist in the prediction of tourism futures. Climate was the principal force driving seasonal patterns of visitation in equatorial, tropical, desert, grassland and temperate zones, whereas visitation to alpine/sub-alpine areas was driven by a complex array of natural and institutional factors. Tourism seasonality was driven mostly by institutional factors only in the sub-tropical climate zone. These analyses suggest that seasonal characteristics of current visitation could be used to predict the degree to which changes in climate and/or institutional arrangements, such as school holiday periods, might influence tourism opportunities in protected areas in eastern Australia.