The reproductive cycle of the sea urchin Paracentrotus lividus was studied in three sites situated in differently polluted locations near Algiers. Gonad indices and histological examination demonstrated a different pattern in the reproductive cycle between the population closest to the Algiers metropolis and the population situated outside the Algiers Bay. The former presented a clear yearly cycle with a high gonad index in spring followed by a spawning period. The latter showed a succession of smaller gonad indices and spawning periods throughout the year. Comparison of the three populations indicated that the higher the pre-spawning gonad increase, the lower the number of spawnings per year. The reproductive cycle was studied over two years that differed in seawater temperature. The 2-year comparison suggested that an early rising sea temperature triggered more precocious spawning, and higher spring and summer temperatures prolonged the spawning period. The pollution level did not act on the gonad index intensity.