The author attempts both to evaluate the data preserved by the register books of various Ljubljana parishes in the second half of the 17th century and to establish certain characteristics in the population development. Consequently he establishes the negative growth of population (the birthrate amounting to 40.78 %, the death-rate up to 44.9 %), the average age of 21 years for brides and 29 for bridegrooms (which, according to the author, is too high), the modal interval of 9 to 18 month between the marriage and the first childbirth. Along with numerous other calculations and data, the author calls the reader’s attention to the methodological predicament in calculating the statistical average as well as to the source insufficiency.