Human cytomegalovirus (HCMV) infection promotes a persistent expansion of a functionally competent NK‐cell subset expressing the activating CD94/NKG2C receptor. Factors underlying the wide variability of this effect observed in HCMV‐seropositive healthy individuals and exacerbated in immunocompromized patients are uncertain. A deletion of the NKG2C gene has been reported, and an apparent relation of NKG2C genotype with circulating NKG2C+ NK‐cell numbers was observed in HCMV+ children. We have assessed the influence of NKG2C gene dose on the NK‐cell repertoire in a cohort of young healthy adults (N = 130, median age 19 years). Our results revealed a relation of NKG2C copy number with surface receptor levels and with NKG2C+ NK‐cell numbers in HCMV+ subjects, independently of HLA‐E dimorphism. Functional studies showed quantitative differences in signaling (i.e. iCa2+ influx), degranulation, and IL‐15‐dependent proliferation, in response to NKG2C engagement, between NK cells from NKG2C+/+ and hemizygous subjects. These observations provide a mechanistic interpretation on the way the NKG2C genotype influences steady‐state NKG2C+ NK‐cell numbers, further supporting an active involvement of the receptor in the HCMV‐induced reconfiguration of the NK‐cell compartment. The putative implications of NKG2C zygosity over viral control and other clinical variables deserve attention.