The article reconsiders the nature and location of science in the development of genetic classification. Drawing on field studies of medical genetics, we explore how patient categorization is accomplished in between the clinic and laboratory. We focus on dysmorphology, a specialism concerned with complex syndromes that impair physical development. We show that dys-morphology is about more than fitting patients into prefixed diagnostic categories and that diagnostic process is marked by moments of uncertainty, ambiguity, and deferral. We describe how different forms (...) of evidence are brought into play and how patterns of physical features are identified as genetic or not. We suggest that clinical categorical work helps articulate the genetic as an emergent domain of medical classification and that moments of ambiguity and deferral create an imperative space that helps legitimate the need for more technoscience, and consequently, more clinical judgment with which to fix the genetic future. (shrink)