Fly and bottom ashes from fuel oil power plants and oil refineries may contain hazardous trace elements, such as heavy metals, which have a negative impact on the environment with time due to potential leaching through acid rains and into groundwaters. This study provides levels of As, Cr, Cu, Hg, Mn, Ni, Pb, Ti, V and Zn of bottom ashes from a thermal power plant and an oil refinery placed in Cienfuegos Bay, Cuba. Trace elements were measured using X-ray fluorescence (XRF) with a SPECTOR X-LAB PRO 2000 system. High contents of Cr, Ni, Pb, Ti, V and Zn were found in the ashes, with values significantly higher than those reported in literature. According to Cuban regulations these ashes are classified as hazardous waste. For this reason we discuss some management alternatives. This study represents the first report of heavy metals in bottom ashes from power plants and oil refineries in Cuba. (C) 2011 Elsevier Ltd. All rights reserved.