Preliminary quantitative data are provided on the latest stage of development and morphological evolution of the closed atoll Vahitahi, in the eastern Tuamotus. From before 4300 to at least 2400 yrs B.P. sea level was at least 0.7 m higher than at present. During this time the development of a flat reef pavement, now slightly emerged, gradually separated the lagoon from the ocean. At about 1200 yrs B.P. the water level of the lagoon, already closed, was still slightly above the present level. The response of the reef was a rapid upward accretion until about 3000 yrs B.P., then an oceanward development at rates averaging from 0.04 to 0.13 m yr −1 .