  Aims. The photometric validation of the Gaia DR1 release of the ESA Gaia
mission is described and the quality of the data shown. Methods. This is
carried out via an internal analysis of the photometry using the most constant
sources. Comparisons with external photometric catalogues are also made, but
are limited by the accuracies and systematics present in these catalogues. An
analysis of the quoted errors is also described. Investigations of the
calibration coefficients reveal some of the systematic effects that affect the
fluxes. Results. The analysis of the constant sources shows that the
early-stage photometric calibrations can reach an accuracy as low as 3 mmag.
