http://www.ttfse.org/default.aspx?p=23&c=85:
Ethnic groups (according year 1991 census): Bosniak 43,5%, Serbs 31,2%, Croats 17,4%, Yugoslavs 5,6%, Montenegrians 0,2%, Macedonians 0,1%, Albanians 0,1%, Others 0,8%, Not declared nationally 0,3%, Unknown 0,8%
And Croats say that their population in Bosnia is now lower. Many of them were settled purposely by Tudjman in Croatian Serb homes and apartments. You might say that the Serbs are in their houses in Bosnia, but most of these Bosnian Croats now in Croatia came from areas in Central Bosnia and left during the Croat-Muslim fighting. (See Croat site: http://www.hercegbosna.org/engleski/cromusl.html
The current CIA factbook uses 2000 figures and has the Muslims at 48%, the Serbs at 37.1%, and the Croats at 14.3%. I do not know if Krajina Serbs from Croatia, who are now in Bosnia, are included in the numbers. The Bosnian government chose not to take an official census in 2001 or 2002 when other ex-Yu republics - Slovenia, Croatia, Serbia, and Macedonia did - so the true percentage may or may not be significantly different than the current figures.