INTRODUCTION. On May 17, at about 6:00 a.m., the Llaima volcano began a strombolian eruption, 10 years since the last short phreatomagmatic eruption (April 1984). The Llaima volcano is a complex composite-shield volcano, with a buried caldera and 40 parasitic scoria cones. It is one of the largest volcanoes in the Southern Andes, covering an area of ca. 500 km2 and with a volume of ca. 400 m3 (Naranjo and Moreno, 1991). Together with Villarrica (Chile) and Sangay (Ecuador) volcanoes, Llaima is one of the most active in the Andes and shows a permanent fumarole in its open summit crater. It is mainly composed of basaltic to andesit e lava flows (51-59% SiO2), although early postglacial deposits include a voluminous andesitic pyroclastic flow (the Curacautin ignimbrite ~24 km3; 13,200 yr. B.P.), surges and a remarkable dacitic plinian pumice fall (-4 km3; 8,800 yr. B.P.), the latter being the most silicic product of the volcano (Moreno and Naranjo, 1991). Since 1640, about 47 eruptions have been reported, 1957 being the year of the last big lava eruption. Most of the eruptive events have generated lahars, and the most hazardous river valleys have been Captren (north) and Trufultruful (southeast) during the 20th century. Though the western slope is covered by the largest glacier, the Lanlan and Calbuco river valleys have also been affected by lahars in recent times (Moreno and Naranjo, 1991). This note aims at describing the most recent eruption of the Llaima volcano that took place on May 17-19, 1994.