The aim of the study was to assess neonatal birth weight (BW) differences between inland and littoral Croatia, to identify BW groups with most pronounced differences, and possible variations in the rate of BW > or = 4000 g between Sibenik area and the rest of littoral (counties with access to the Adriatic Sea) and inland Croatia. The study included data on 99.42% of 200,740 live births recorded in 37 Croatian maternity hospitals during the 2001-2005 period. Distribution of 500-g BW groups was analyzed irrespective of neonatal sex and gestational age. Differences were found between the inland and littoral parts of Croatia according to distribution of the BW groups of < 2500 g (5.4% vs. 4.4%), 2500-3999 g (84% vs. 80.2%) and > or = 4000 g (10.6% vs. 15.4%) (chi2 = 882; p < 0.001).The highest rate of BW > or = 4000 g was recorded in Sibenik-Knin County (5-year mean 18.32%) and was greater throughout the littoral as compared with inland Croatia (5-year mean 14.99% vs. 9.58%). A shift towards higher BWgroups recorded throughout littoral as compared with inland Croatia supports the hypothesis on variation in anthropologic characteristics in the respective populations to be pronounced as early as at birth. Study results confirmed fetal macrosomia not to be exclusively characteristic of Sibenik-Knin County, since the rate of neonatal BW > or =4000 g was significantly higher in the entire littoral as compared with inland Croatia.