The temperature and concentration dependence of the refractive index, n (D)(x, T) , in ethanol-water mixtures agrees with previous data in the ethanol-rich concentration range. The refractive index versus concentration x determined at 20 (A degrees) C shows the expected maximum at about 41 mol% water (22 mass% water). The temperature derivative of the refractive index, dn (D) /dT, shows anomalies at lower water concentrations at about 10 mol% water but no anomaly at 41 mol% water. Both anomalies are related to intermolecular interactions, the one in n(D) seems to be due to molecular segregation and cluster formation while the origin of the second one in dn (D) /dT is still not clear.