We investigated the value of procalcitonin kinetics as a prognostic marker during ventilator-associated pneumonia (VAP). This prospective, observational study was conducted in a medical intensive care unit in a university hospital. All consecutive patients with microbiologically proven VAP who survived 3 days after its diagnosis were included and grouped according to clinical outcome: favorable or unfavorable, defined as death, VAP recurrence, or extrapulmonary infection requiring antibiotics before Day 28. Serum procalcitonin levels were measured on Days 1, 3, and 7 for all patients. Among the 63 patients included, 38 had unfavorable outcomes. On Day 1, they were more critically ill than patients with a favorable outcome. Serum procalcitonin levels decreased during the clinical course of VAP but were significantly higher from Day 1 to Day 7 in patients with unfavorable outcomes. Multivariate analyses retained serum procalcitonin levels on Days 1, 3, and 7 as strong predictors of unfavorable outcome. Based on these data, procalcitonin could be a prognostic marker of outcome during VAP.