This paper reports and discusses 'genomic designation' as a way of classifying people. In genomic designation the object of biomedical analysis--and the concomitant medical category that is subject to scientific, clinical, and social action--is delineated on a genomic basis, while the phenotype is decentralized and tabulated post factum. Unlike prominent sociological concepts such as biosociality or geneticization, where genetic proclivities for or explanations of phenotypic categories affect social processes, genomic designation treats characteristics of the genome as the essential referent of new categories of illness. I outline the relevant sociological literature and the shift to what Nikolas Rose has called the 'molecular gaze' before explicating the concept ofgenomic designation and its half-century history. I use 22q13 Deletion/Phelan-McDermid syndrome as an example of genomic designation: investigations into the deletion of genetic material at site q13 on the 22nd chromosome preceded and made practicable the delineation of a syndrome more than a decade later, even though the associated phenotype is not distinct enough for diagnosis. Finally, I discuss the implications of this turn to 'rigidly designate' kinds of people according to observations made at the level of the genome and outline directions for future research.