Marine invertebrates in the Caribbean basin have experienced several severe epizootic events in recent decades that have resulted in population collapse of the impacted species. The well-documented die-off episode of the long-spined sea urchin Diadema antillarum (Philippi, 1845) in the early 1980s, stands out among these events. The collapse in this keystone species resulted in a significant top-down trophic cascade in which macroalgae cover increased significantly, altering the reef community. Nearly 40 years later, Diadema populations in many localities have not recovered to pre-die-off density levels. Early in 2022, a new mortality event of D. antillarum has been reported in the U.S. Virgin Islands and eastern Puerto Rico. Preliminary observations in several localities in Culebra Island (midway between USVI and PR) indicate that close to 90% of the urchins are dead. However, mortality has not been observed yet on the main island of Puerto Rico.