Cross-calibration is a fully automated algorithm for calibration of interferometric synthetic aperture radar (IFSAR) data. It has been developed for single-pass interferometry, but the principles may be applicable to multi-pass interferometry, too. The algorithm is based on natural distributed targets and it excels by neither requiring surveyed ground control points nor dedicated calibration scenes. However, the parameters to be calibrated must be stable during mapping. The algorithm has been applied to data from the Danish airborne SAR, EMISAR, and the performance has been assessed. The algorithm appears to be fairly robust with respect to the terrain type. However, the result of the calibration may deteriorate if the terrain elevation, as measured with the SAR, changes systematically with the incidence angle or the aspect angle.