We estimate the total number of volunteers from Belgium at 2,400, of whom 1,600 held Belgian nationality. This estimate is, of course, supported by the personal data in the database. Regarding the origin of the Belgian volunteers, there are notable differences between regions. According to the latest calculations, Wallonia provides 63% of the volunteers, Flanders 22%, and Brussels 15%. Compared to population numbers, Flanders is underrepresented, and Wallonia is clearly overrepresented among the volunteers. A comparison that provides an indication of the identity of the volunteers is the national distribution of the electoral results of the Communist Party in 1936: 59% for Wallonia, 19% for Flanders, and 22% for Brussels.

As for the foreigners who left from Belgium, the following estimates are realistic: 245 Poles (excluding the 'Poles' of Jewish origin), about 200 Yiddish-speaking Jews of various nationalities (mainly from Poland and Russia and the regions that belonged to the Austro-Hungarian Dual Monarchy before World War I), 165 Italians, and various other nationalities, among which Germans, Romanians, Czechs, and Yugoslavs are the most numerous. This relatively significant group of foreigners reflects a dual reality in Belgium during the interwar period: on the one hand, the presence of political refugees from fascist Italy and Nazi Germany, and on the other hand, the influence of leftist tendencies within the migrant communities (Polish and Italian miners, Jewish diamond and leather workers, but also students).

Of these 2,400 volunteers, it is certain that 287 of them did not survive their involvement in the Spanish Civil War. This gives us an average figure of approximately 12% fatalities.