A measurement is presented of the associated production of a single top quark and a Z boson. The study uses data from proton–proton collisions at s=13TeV recorded by the CMS experiment, corresponding to an integrated luminosity of 35.9 fb −1 . Using final states with three leptons (electrons or muons), the tZq production cross section is measured to be σ(pp→tZq→Wbℓ+ℓ−q)=123−31+33(stat)−23+29(syst)fb , where ℓ stands for electrons, muons, or τ leptons, with observed and expected significances of 3.7 and 3.1 standard deviations, respectively.