The asterinid sea star Patiriella vivipara is endemic to southeast Tasmania and has a highly restricted distribution, being only known from four locations. It has an unusual pattern of viviparous reproduction, giving birth to juveniles. In this study the birth rate, growth rate, size and age at commencement of reproduction of P. vivipara was examined in aquaria for a period of six years. The population of P. vivipara at Pittwater was also monitored through monthly examination of a permanent 1m2 quadrat in which the number of adults and juveniles were counted and recorded. These counts were made over an eight-year period. Patiriella vivipara gives birth to juveniles through the year with a period of enhanced reproduction from November to January. Records of water salinity and temperature were taken at Pittwater, as were air temperatures and exposure times during low tide.