The reproductive behavior and movements of arribada nesting olive ridley turtles (Lepido- chelys olivacea) were studied during the 1990 and 1991 nesting seasons (September through November) at Nancite Beach, Santa Rosa National Park, Guanacaste, Costa Rica. Females that normally emerge synchro- nously once a month on Nancite Beach to oviposit delayed oviposition in response to a period of very heavy rainfall. Females retained oviducal eggs for 63 days and emerged synchronously to oviposit at Nan- cite Beach after the rain had ceased. Egg retention in L. olivacea appears to be an adaptation which en- ables delayed oviposition when environmental conditions are unsuitable and may also facilitate reproduc- tive synchrony. We suggest that preovipositional arrest of developing embryos may have occurred while oviducal eggs were retained.