This catalogue is an update of the previous versions. The recent release of the final release of the 2dF quasar catalogue and of the first part of the SLOAN catalogue, almost doubling the number of known QSOs, led us to prepare an updated version of our Catalogue of quasars and active nuclei, which now contains 48921 quasars, 876 BL Lac objects and 15069 active galaxies (including 11777 Seyfert 1). Like the tenth edition, it includes position and redshift as well as photometry (U, B, V) and 6 and 11 cm flux densities when available. The present edition this catalogue contains the quasars with measured redshift known prior to August 1st, 2003. Version history: (1) Veron-Cetty M.P., Veron P., 1984, ESO Scientific Report 1 (2) Veron-Cetty M.P., Veron P., 1985, ESO Scientific Report 4 (3) Veron-Cetty M.P., Veron P., 1987, ESO Scientific Report 5 (Catalogue <VII/93>) (4) Veron-Cetty M.P., Veron P., 1989, ESO Scientific Report 7 (Catalogue <VII/126>) (5) Veron-Cetty M.P., Veron P., 1991, ESO Scientific Report 10 (Catalogue <VII/146>) (6) Veron-Cetty M.P., Veron P., 1993, ESO Scientific Report 13 (Catalogue <VII/166>) (7) Veron-Cetty M.P., Veron P., 1996, ESO Scientific Report 17 (Catalogue <VII/188>) (8) Veron-Cetty M.P., Veron P., 1998, ESO Scientific Report 18 (Catalogue <VII/207>) (9) Veron-Cetty M.P., Veron P., 2000, ESO Scientific Report 19 (Catalogue <VII/215>) (10) Veron-Cetty M.P., Veron P., 2001, Astron. Astrophys. 374, 92 (Catalogue <VII/224>)