Prescribed burning is a tool for reducing fuels and restoring a disturbance process to landscapes that historically experienced fire. It is often assumed, or at least desired, that the effects of prescribed burns mimic those of natural fires. However, because of operational and liability constraints, a significant proportion of prescribed burning is, in many ecosystems, conducted at different times of the year than when the majority of the landscape burned historically. This has brought into question the extent to which prescribed fire mimics effects of the historical fire-disturbance regime, and whether there are any negative impacts of such out-of-season burning. Prescribed burning may be conducted at times of the year when fires were infrequent historically, leading to concerns about potential adverse effects on vegetation and wildlife. Historical and prescribed fire regimes for different regions in the continental United States were compared and literature on season of prescribed burning synthesized. In regions and vegetation types where considerable differences in fuel consumption exist among burning seasons, the effects of prescribed fire season appears, for many ecological variables, to be driven more by fire-intensity differences among seasons than by phenology or growth stage of organisms at the time of fire. Where fuel consumption differs little among burning seasons, the effect of phenology or growth stage of organisms is often more apparent, presumably because it is not overwhelmed by fire-intensity differences. Most species in ecosystems that evolved with fire appear to be resilient to one or few out-of-season prescribed burn(s). However, a variable fire regime including prescribed burns at different times of the year may alleviate the potential for undesired changes and maximize biodiversity.