[en] The measured values of monthly average daily global H-bar and diffuse H-bar_d solar radiation on a horizontal surface, as well as the number of bright sunshine hours n-bar, for four Egyptian locations are analyzed. The selected locations include Matruh, Al-Arish, Rafah and Aswan to represent the weather conditions of the north and south of Egypt. First, second and third order correlations between the diffuse fraction H-bar_d/H-bar and the clearness index K-bar_t and also between the diffuse transmittance H-bar_d/H-bar₀ and the maximum relative number of bright sunshine hours n-bar/N-bar have been proposed for the selected locations using the method of regression analysis. Comparisons between the measured and calculated values of H-bar_d show that a first order correlation between H-bar_d/H-bar and K-bar_t can be used for estimating H-bar_d at the present locations with good accuracy. However, second order correlations between H-bar_d/H-bar or H-bar_d/H-bar₀ and n-bar/N-bar are recommended for estimating H-bar_d at these locations. For all locations, the relative percentage errors for a single month rarely exceed ±10%. Furthermore, the data available from the four locations are combined and employed to develop correlations that may be applied for any Egyptian location. All Egypt correlations are found to be able to predict the annual averages of horizontal diffuse radiation with excellent accuracy. Therefore, the long term performance of solar energy devices can be estimated