Kīlauea may be one of the world's most intensively monitored volcanoes, but its eruptive history over the past several thousand years remains rather poorly known. Our study has revealed the vestiges of thin basaltic tephra deposits, overlooked by previous workers, that originally blanketed wide, near-summit areas and extended more than 17 km to the south coast of Hawai'i. These deposits, correlative with parts of tephra units at the summit and at sites farther north and northwest, show that Kīlauea, commonly regarded as a gentle volcano, was the site of energetic pyroclastic eruptions and indicate the volcano is signifi cantly more hazardous than previously realized. Seventeen new calibrated accelerator mass spectrometry (AMS) radiocarbon ages suggest these deposits, here named the Kulanaokuaiki Tephra, were emplaced ca. A.D. 400-1000, a time of no previously known pyroclastic activity at the volcano. Tephra correlations are based chiefl y on a marker unit that contains unusually high values of TiO 2 and K 2 O and on paleomagnetic signatures of associated lava fl ows, which show that the Kulanaokuaiki deposits are the time-stratigraphic equivalent of the upper part of a newly exhumed section of the Uwēkahuna Ash in the volcano's northwest caldera wall. This section, thought to have been permanently buried by rockfalls in 1983, is thicker and more complete than the previously accepted type Uwēkahuna at the base of the caldera wall. Collectively, these fi ndings justify the elevation of the Uwēkahuna Ash to formation status; the newly recognized Kulanaokuaiki Tephra to the south, the chief focus of this study, is defi ned as a member of the Uwēkahuna Ash. The Kulanaokuaiki Tephra is the product of energetic pyroclastic falls; no surge-or pyroclastic-fl ow deposits were identifi ed with certainty, despite recent interpretations that Uwēkahuna surges extended 10-20 km from Kīlauea's summit.