ABSTRACT: Intentional harm to marine mammals refers to deliberate human actions that cause injury, suffering, or death, and it is illegal in many countries. These actions often result from direct human attacks and are motivated by various reasons, with retaliation by fishermen being the most common. Such attacks cause severe tissue damage, frequently leading to the debilitation or death of the targeted animal. In this report, we document 13 cases of intentionally harmed marine mammals: 12 bottlenose dolphins Tursiops truncatus and 1 Mediterranean monk seal Monachus monachus found in the Croatian part of the Adriatic Sea between 1990 and 2023. Our analysis includes the life history data of the attacked specimens, post-mortem findings, and the weaponry involved. Among 311 post-mortem examinations conducted, 4.2% revealed intentional harm. Adult male bottlenose dolphins were most frequently targeted (46.2%), with a majority (53.8%) succumbing immediately due to exsanguination. Shotgun pellets, bullets, and underwater speargun spearheads were recovered from their carcasses. The attacks occurred with no discernible seasonal pattern; however, 61.5% of the cases were recorded from Istria County. Our findings underscore the inadequacy of current surveillance and enforcement in protecting marine mammals from deliberate harm. We advocate for the implementation of educational initiatives targeting relevant groups, intensive sea patrols, and routine inspection of weapons with high penalties for illegal possession and misuse, all reinforced by media campaigns to combat this malicious human behaviour.