A new occurrence of the hydrozoan Olindias muelleri and the first case of an associated envenomation were recorded from the eastern Aegean Sea. A total of eight adult medusae of O. muelleri were collected near the surface on 22 and 23 June 2018 in Boyalik Bay, Turkey following a sting report by a bather. Medusae were identified as O. muelleri using morphological keys and confirmed through COI-based DNA barcoding. The presence of O. muelleri may have not been noticed in the past in the region or it could stem from a recent range expansion from other parts of the Mediterranean Sea. Monitoring is needed to better understand the spread of O. muelleri and the threat it presents for human health and coastal tourism in Cesme.