Human natural killer (NK)–cell repertoires are biased toward more frequent expression of inhibitory killer cell Ig-like receptor (KIR) receptors for self-human leukocyte antigen (HLA) class I. Moreover, only those NK cells that express cognate receptors for self are fully functional in terms of cytotoxicity and cytokine production. It is so far unknown whether functional education and structural adaptation to HLA class I are implemented during NK-cell development and whether both processes are mechanistically connected. Here we show that NK-cell repertoires in cord blood are not yet shaped toward increased clonal frequencies of KIR for self-HLA class I as determined for the 3 major KIR ligands C1, C2, and Bw4. Nonetheless, neonatal NK cells expressing cognate KIR exhibited enhanced effector function on the level of degranulation and cytokine production. The study suggests that functional education of cognate KIR by self-HLA class I precedes structural adaptation of KIR repertoires and that both processes are not directly linked to each other.