Over the past four decades, Farrell has investigated the benefits, risks, tests, and costs of early diagnosis of cystic fibrosis (CF) through newborn screening. The stimulus for this unique investigation, initiated in 1984, came from Farrell’s experiences practicing neonatology and pediatric pulmonology concurrently. The initiative’s results led to nationwide screening for CF by 2010, with most states using the immunoreactive trypsinogen (IRT) and DNA method developed in Wisconsin. This was the first U.S. population-based application of molecular genetics testing.