Sex-biased maternal investment involves differential allocation of resources to production and rearing of sons or daughters as a function of their anticipated reproductive output. We examined reproductive investment among captive giraffes (Giraffa camelopardalis) over a 21-year period to determine extent to which females invest differentially in offspring by sex. We found an unbiased sex ratio at birth and comparable interbirth intervals following rearing of either sons or daughters. Early neonatal mortality compressed interbirth interval and females probably conceived while lactating. We suggest that females invest equally in sons and daughters because males surpass females in size subsequent to the period of infant dependency.