Treatment with granulocyte colony-stimualting factor (G-CSF) increases neutrophil counts in periparturient cows.The aim of this experiment was to evaluate the effects of treating Holstein cows with pegbovigrastim on periparturient diseases, milk production, and reproductive performance. Cows were randomly allocated into 1 of 2 treatment groups: untreated control (CTR, n = 423) and pegbovigrastim (PEG, n = 417). At 7 d from anticipated calving date (d −7), cows allocated to PEG received a subcutaneous injection containing 15 mg of pegylated recombinant bovine G-CSF (pegbovigrastim injection, Imrestor, Elanco Animal Health). A second injection was administered within 24 h after calving (d 0). Blood samples were obtained from a subset of cows at −7 d, and at 0, 3, 7, and 14 d relative to parturition. Samples were used for hemogram and quantification of haptoglobin, nonesterified fatty acids, and β-hydroxybutyrate concentrations. Postpartum disease occurrence was recorded from calving until 30 DIM. Milk yield was recorded for the first 12 wk after calving. Multivariable mixed models were performed using repeated measures ANOVA, logistic regression, or proportional hazard models. PEG-treated animals exhibited 3- to 4-fold increase in circulating granulocyte, lymphocyte, and monocyte numbers 3 d after treatment, and this increase decreased over time but always remained significantly higher compared with CTR. The administration of PEG was not associated with clinical and subclinical mastitis, retained placenta, metritis, and endometritis. Primiparous cows treated with PEG tended to have lower odds of developing hyperketonemia than CTR. PEG cows tended to have higher odds of being diagnosed with puerperal metritis compared with CTR. Cows treated with PEG had higher odds of being diagnosed lame within 30 DIM compared with CTR. Primiparous cows treated with PEG produced more milk than CTR primiparous cows during the first 12 wk postpartum. Treatment did not alter reproductive performance. We conclude that treating dairy cows with PEG did not influence periparturient disease incidence, increased milk yield in primiparous cows, and did not influence reproductive performance.