The "immigrants problem", with the inevitable social aspects which this new phenomenon involves, has grown lately into a matter of primary interest to the public opinion of our country. The hospital too, in its capacity as leader among the sociosanitary institutions, has witnessed a change to some extent of the demand for services resulting from this reality. The Authors intend therefore to re-define here the whole body of a large metropolitan hospital patients, referring to an extensive statistical information and analyzing with special attention the statistics about foreign citizens. To this purpose they have considered all the cases of hospitalization occurred during a five-year period, from 1985 to 1989. The gathered data have been elaborated and analyzed from a more strictly demographic standpoint and (in particular) from the epidemiological point of view, comparing the data resulting among the immigrants with those regarding the whole body of hospitalized people during the same period. The data so obtained show, in spite of some significant differences due almost certainly to social differences, a superimposition on the italian reality, reproducing on a smaller scale its distinctive features. Even if this research is restricted to a specific situation, the results obtained can be considered a basis to make further similar studies within other hospital structures, in order to point out the different and variable demands for hospital services originating from this new social reality.