Dr. Greenberg is a nationally recognized leader in neonatal-perinatal medicine. He serves as director of the Division of Neonatology for Cincinnati Children's Hospital Medical Center leading one of the largest comprehensive clinical and academic programs for newborn care in the United States. Dr. Greenberg has been division director since 2003, and has been an active clinician, researcher and teacher at Cincinnati Children's Hospital Medical Center for more than 22 years. In 2009, he was appointed associate director of the Perinatal Institute at Cincinnati Children’s and became co-director in 2011.

His research activities include developmental biology of the lung, neonatal chronic lung disease, neonatal epidemiology, and prevention of preterm birth. Dr. Greenberg partners with Cincinnati Children's faculty and regional leaders to lead community health initiatives to reduce preterm birth and eliminate infant mortality. He has authored more than 30 original research articles; and six book chapters in the textbook of Pediatrics, Maternal-Fetal Medicine, and Pulmonology.

As medical director for Regional Newborn Services and division director, Dr. Greenberg led the dramatic growth of the neonatology clinical program from 12 faculty physicians providing care at two neonatal intensive care units (NICUs) to more than 50 physicians providing newborn care at 13 regional hospitals including the five NICUs. The Division of Neonatology now has over 120,000 patient encounters per year. In addition to caring for all of the Level III and Level II intensive care nursery patients in the region, division physicians also see more than 18,000 normal newborns every year. The Newborn Intensive Care at Cincinnati Children’s represents the hub of the neonatology clinical program. This NICU has over 750 admissions per year and focuses its activities on caring for infants with complex medical and surgical problems. All patients requiring surgery, surgical subspecialty care, complex radiographic imaging, or comprehensive diagnostic services are managed at the Cincinnati Children's Hospital Medical Center NICU.

In addition to the clinical program, the Division of Neonatology has an active research program. The division is one of the 22 NICHD Neonatal Research Network Centers. Extramural grant funding for the division in fiscal year 2015 was in excess of $10 million. Division research programs span basic, translational, and clinical endeavors.

The division also has an active quality improvement program focusing on outcomes in varied clinical settings ranging from improving reliability of delivery room thermal stability to reduction of central-line-associated blood stream infections in the NICU.