Spawning of the Mediterranean dusky grouper Epinephelus marginatus (Lowe, 1834) was observed for the first time in summer 1996 during scuba diving surveys in the Medes Islands Marine Reserve (NW Mediterranean). Ten spawning events were observed, which occurred at sunset, in the evenings around the new moon of August. A mature female (usually between 50 and 75 cm TL), in the standard mottled colour pattern, and a larger (more than 100 cm long) dominant male, in a conspicuous silver streaked colour-pattern, ascended up to 12 m side by side, spiralling in an anti-clockwise direction two or three times, from the bottom to shallow warmer waters, where the ova and sperm are released. Some traits of variability over this common pattern of spawning are described. Predation by saddled bream Oblada melanura, which concentrate in great numbers after each spawning suggests a very low survival of the spawned eggs.