Typical solar radiation data are very important as input in modelling, designing and performance evaluation of solar energy applications. In this study, typical solar radiation data were obtained for Istanbul, Turkey both from measured data and synthetic generation. Firstly, a test reference year for daily global solar radiation on a horizontal surface was generated using 19 years measured data. The daily global solar radiation as typical data for Istanbul was presented throughout a year in a tabular form. Secondly, the daily global solar radiation for Istanbul was expressed with a trigonometric equation using long-term measured data. It is expected that the typical data and the equation derived will be useful to the designers of solar energy systems as well as those who need to have fairly good estimates of daily global solar radiation for Istanbul. Copyright (C) 2003 John Wiley Sons, Ltd.