A total of 1125 specimens of sardine, Sardina pilchardus, ranging in total length from 4.9 to 12.5 cm (mean 8.31 ± 1.41 cm) and in weights between 1.02 g and 11.18 g (mean 4.40 ± 1.87 g) were randomly sampled using a beach seine from the Krka River estuary. Samples were collected monthly according to their occurrence in this area from October to February during 2002/03, 2003/04 and 2004/05, which is during the spawning period of this species. Monthly fluctuations in the length frequency distributions of sardine were observed during that time. The length–weight relationship of all sardine specimens was described by the equation: W = 0.007 L 2.9587 ( r 2 = 0.9626); and the isometric nature of relative growth was established ( t = −5.1495; p < 0.05). According to the allometric condition factor K a, sardine specimens were in better somatic condition at the beginning of their appearance (spawning period) in the Krka River estuary. The length at which 50% of sardines were mature ( L 50) was calculated to be 7.9 cm.