Rhopilema nomadica is an Indopacific scyphomedusan, which has migrated into the eastern Mediterranean in recent years. Large aggregations of the medusae were recorded in Haifa Bay, Israel, reaching 5.5×105 medusae per square nautical mile during summer 1989. The life cycle of R. nomadica from planula to young medusa is described. Fertilization is external and planulae are formed within a few hours at 20°C. After settlement, polyps were fed with Artemia sp. nauplii and developed into polydisc strobilae within 45 d. The strobilation process was completed within 7 d, and the liberated ephyrae developed into young medusae within 2 mo. Asexual reproduction occurred mainly via podocyst formation. The population explosion of R. nomadica could be attributed to its high reproductive potential.