For the first time, we report the occurrence of the irregular echinoid Cassidulus caribaearum (Echinodermata: Echinoidea) in Puerto Rico. This is also the first record of this species in the Greater Antilles. Until then it had only been observed in Costa Rica, Mexico, Panama, Belize, San Marteen and the US Virgin Islands. This novel information increases its previously known distribution range and represents the sixteenth shallow water echinoid occurring in Puerto Rico.