<i>Background:</i> Diagnosis of neonatal early-onset sepsis is difficult because clinical signs and laboratory tests are non-specific. Early antibiotic therapy is crucial for treatment success. <i>Objective:</i> To evaluate the effect of procalcitonin (PCT)-guided decision-making on duration of antibiotic therapy in suspected neonatal early-onset sepsis. <i>Methods:</i> This single-center, prospective, randomized intervention study was conducted in a tertiary neonatal and pediatric intensive care unit in the Children’s Hospital of Lucerne, Switzerland, between June 1, 2005 and December 31, 2006. All term and near-term infants (gestational age ≧34 weeks) with suspected early-onset sepsis were randomly assigned either to standard treatment based on conventional laboratory parameters (standard group) or to PCT-guided treatment (PCT group). Minimum duration of antibiotic therapy was 48–72 h in the standard group, whereas in the PCT group antibiotic therapy was discontinued when two consecutive PCT values were below predefined age-adjusted cut-off values. <i>Results:</i> 121 newborns were randomly assigned either to the standard group (n = 61) or the PCT group (n = 60). The two groups were similar for baseline demographics, risk factors for early-onset sepsis, likelihood of infection as assessed by the attending physician and early conventional laboratory findings. There was a significant difference in the proportion of newborns treated with antibiotics ≧72 h between the standard group (82%) and the PCT group (55%) (absolute risk reduction 27%; odds ratio 0.27 (95% CI 0.12–0.62), p = 0.002). On average, PCT-guided decision-making resulted in a shortening of 22.4 h of antibiotic therapy. Clinical outcome was similar and favorable in both groups but sample size was insufficient to exclude rare adverse events. <i>Conclusion:</i>Serial PCT determinations allow to shorten the duration of antibiotic therapy in term and near-term infants with suspected early-onset sepsis. Before this PCT-guided strategy can be recommended, its safety has to be confirmed in a larger cohort of neonates.