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Many social variables affect breast-feeding patterns, but naturally due to biological constraints, breast-feeding practice cannot be altered limitlessly to suit social norms. A common functional “shape” might therefore be expected to describe breast-feeding discontinuation probabilities by age in various societies. If such a common functional form were to exist, the situation would be analogous to that with birthweight distributions: birthweights in different populations vary with respect to mean and dispersion, but the distributions they follow are essentially normal curves, i.e., they are members of a single family of curves. We demonstrate here that a common function describes the curves of breast-feeding discontinuation in the United States and in an African population with natural fertility levels. Lesthaeghe and Page (1980) developed a two-parameter model standard curve of the probability of breast-feeding by duration since birth, based on African data. We fitted data from the U.S. National Survey of Family Growth Cycles II and III to their model curve; the U.S. data followed the standard curve quite closely. The findings demonstrate empirically that a common family of monotonically declining curves can describe patterns of breast-feeding discontinuation in quite different societies. Contrasting findings of Ford and Kim concerning durations of post-partum amenorrhea are discussed.