In handball, but also in other team sports, date of birth applies as main criterion for forming competition groups in younger age categories. Competition organization in younger age categories implies merging two consecutive years, and in handball in Croatia until recently the players born in uneven years had been joining to the ones born in even years. With this kind of system, differences between young athletes have become more and more noticeable, because they are often not sharing the same status of maturation, where younger athletes in competition groups are placed in unequal position in regard to older athletes. This phenomenon, caused by chronological age differences is known by the name of relative age, and the consequences are referred to as the relative age effect. The main purpose of this master’s thesis was to determine the level of presence of relative age effect between athletes in same competition groups considering quartal and year of birth, overall length of training time, attendance at trainings, player positions and understanding the handball game. A sample of survey contains considered 107 young handball players placed in currently valid competition groups for younger age categories. Chi-squared tests with significance level of 0,05 were performed to determine if there are significant differences between even and uneven years of birth in relation to the observed variables. Statistically significant differences between the players having even and uneven years of birth were found according to criterion of understanding the handball game (p=0,04) and player positions (p=0,04). From overall 62 boys having uneven year of birth, 33 (53,23%) of them satisfy criterion of understanding the handball game, whereas relatively 29 (46,77%) of them don’t. On the other side, from 45 boys having even year of birth, only 15 (33,33%) of them satisfy the same criterion, relatively 30 (77,77%) of them don’t. Statistically significant difference relating to criterion player positions were found in back attacking positions. From overall 40 attacking back positions, including those having even and uneven years of birth, a ratio of 28 : 12 was obtained in favour of even years, that is 70% in opposition to 30%. Statistically significant differences between those having even and uneven years were not found according to criterion attendance at trainings (p=0,81) and overall length of training time (p=0,14).