The aim of the present study is to analyze the patterns of research collaboration of the National University of Mexico (UNAM) in mainstream literature in relation to its science policy.Sixty percent of the collaborative studies in science of the UNAM registered in the Web of Science from 1999 to 2002 involved only national institutions; the corresponding figure for the social sciences, arts and humanities was 87%.In both cases articles published in international collaboration received more citations on average than those involving only national institutions.Significant levels of coauthorship were found between the UNAM research centres and local institutions in those areas of the country where the UNAM has implemented a policy of decentralization of research activity.Little collaboration was found between institutes of the UNAM in the different research areas, as well as few publications in journals outside their own research areas.Both findings suggest a low level of participation in multi and interdisciplinary projects.