This paper investigates the main characteristics of the atrium and their influence on the daylight conditions in the adjoining space and on the atrium floor. The shape of the atrium and its orientation to the sun, the transmittance of the roof, the reflectivities of the atrium surfaces and the glazed areas are important parameters in the daylighting design of atrium buildings. Several atrium cases, characterized by a different Well Index, are analysed and a simplified methodology used, to predict daylight factor on the atrium floor and in the adjacent rooms, developed through computer simulation using Radiance as a tool. (C) 2004 Elsevier Ltd. All rights reserved.