The Adriatic Sea is inhabited by an endangered and protected population of bottlenose dolphins (Tursiops truncatus). Bottlenose dolphins which are found dead in nature have been examined postmortally since 1990 at the Faculty of Veterinary Medicine, University of Zagreb within the monitoring of marine mammal populations of the Adriatic Sea. Postmortal examinations showed changes in the abdominal wall structure of several specimens. These changes were determined as congenital abdominal wall clefts. This malformation appears in form of a discontinuation of the white line in the umbillical region and a cleft between the left and right rectus abdominis muscle. We analysed data of 326 bottlenose dolphins found from 1990 until 2018 in the Croatian part of the Adriatic Sea. The analysis of postmortal protocols showed that in 9.2% (n=30) dolphins the congenital abdominal wall cleft was recorded. Out of them 48.0% (n=12) were newborns. The prevalence of the congenital abdominal wall cleft was two times higher in females than in males. The prevalence is highest in female newborns (23.3%, n=7). In 36.7% (n=11) dolphins with the congenital abdominal wall cleft other malformations were recoded, namely the patent formane ovale and ductus arteriosus. The eldest dolphin with the congenital abdominal wall cleft was 5 years old which supports the presumption that the aquatic environment positively influences the survival of dolphins with this malformation.