This paper assumes a causal relationship, although poorly discerned and incompletely described, between certain improvements in water supply and sanitation and the nutritional status of older infants and young children (age 8 months to 4 years). Since the debate surrounding this relationship bears not so much on its existence as on its implications for field programs, the paper will be limited to addressing the strengths of the relationship as revealed in studies and the question of whether or not nutritional status can and should be used as an evaluation measure for water supply and sanitation programs. Other issues include the research needed for further clarification of this complex relationship and the implications of current knowledge for policy and program planning. First the importance of the water/sanitation-nutrition relationship, and a conceptual model of this relationship, and then some of the existing evidence will be reviewed. At the close, questions needing further debate will be summarized.