Association of the idoteid isopod, Synidotea variegata Collinge 1917 with the echinoid sea urchin, Stomopneustes variolaris Lamarck, 1816 is reported for the first time from the rocky subtidal region of Vizhinjam coast, southwestern India. Isopods infested the spines and peristome of sea urchins and the intensity of infection increased with the increasing test diameter of the host.