During a three year-period, the participants of a NATO Science for Peace project performed ambient noise measurements inside buildings in four European countries. This paper reports the results relevant to reinforced concrete (RC) buildings with height in the range 1-20 floors. The total number of such buildings surveyed is 244. The most striking feature is the similarity of the height-period relationships in the four countries, which allowed the treatment of the all measurements as a single database. We found no significant correlation with other variables, and calculated a regression that is very similar to other empirical height-period relationships and quite different from code provisions and theoretical models.