Our objectives were to evaluate the association of immediate postpartum blood Ca concentration with metritis and Dairy Herd Improvement Association (DHIA) first test milk production. A total of 314 primiparous (PP) and 1,111 multiparous (MP) cows from 6 herds in New York State were enrolled in a cohort study, and had a blood sample collected within 12 h of parturition. Diagnosis of metritis (defined as a watery, fetid, and reddish-brownish uterine discharge up to 14 d in milk) was performed by farm personnel. The effect of blood Ca concentration on metritis and first test milk yield for PP and MP were analyzed with Poisson regression and linear mixed models, respectively. Herd was included as a random effect in all models. Postpartum Ca concentration was not associated with metritis (10 and 8.5% prevalence in PP and MP, respectively) diagnosis in PP [P = 0.76; while controlling for the effect of retained placenta (RP)] or MP cows [P = 0.21; controlling for RP and parity (2nd versus 3rd or higher)]. Primiparous and MP animals with lower postpartum Ca concentrations produced more milk at first DHIA test than animals with higher Ca concentrations. After dichotomization of the Ca variable using previously reported subclinical hypocalcemia cut-points of 8.0 and 8.4 mg/dL, PP cows with Ca concentrations ≤ 8.0 (8%) and 8.4 (17.5%) mg/dL (controlling for metritis and d in milk at DHIA test) produced 4.0 kg (P = 0.006) and 2.4 kg (P = 0.01) more milk, respectively, than PP animals with Ca concentrations > 8.0 and 8.4 mg/dL at first DHIA test. Multiparous cows with Ca concentrations ≤ 8.0 (51%) and 8.4 (68%) mg/dL (controlling for metritis, displaced abomasum, parity, and d in milk at DHIA test) produced 1.8 kg (P = 0.002) and 1.5 kg more milk (P = 0.01), respectively, than MP animals with Ca > 8.0 and 8.4 mg/dL at first DHIA test. In our study, immediate postpartum Ca concentration had no association with metritis diagnosis, and cows with lower blood Ca concentration produced more milk in early lactation compared with cows with higher blood Ca concentrations.