We examined whether large floods and droughts are worsening. We developed a 300-year long record of extreme flows by reconstructing past events from tree-ring records (drought) and flood sediment deposits to supplement instrumented flow records. Droughts have become more severe in the last century, but large floods have decreased in size and frequency since the 1800s CE. Droughts and large floods frequently occurred in close sequence over the entire period of record, suggesting shifts from droughts to large floods is a persistent pattern. Frequency analyses used to estimate the future occurrence of extreme flows may underestimate their associated risks if only short, instrumented records are relied upon to represent extreme events.