Most critiques of evidence-based medicine (EBM) focus on the scientific shortcomings of the technique. Social scientists are more likely to criticize EBM for its ideological biases, a criticism that makes sociological sense but is difficult to substantiate. Using evidence from the scientific debate over maternity care in the Netherlands--where nearly one-third of births take place at home--the author shows that research evidence is the product of a researcher's assumptions about the practice in question. In the case of maternity care in the Netherlands, ideological differences about the most appropriate way to give birth--based in the researcher's clinical experience--give rise to irresolvable disagreements about what constitutes evidence and how that evidence is to be interpreted. "Evidence" cannot settle scientific disputes in any simple way. Rather, it becomes a rhetorical justification for whatever particular groups were going to do anyway. Scientific evidence rests on clinical practice, which in turn is rooted in structural arrangements and cultural ideas.