Background: The long pentraxin PTX3 is a key component of the humoral arm of innate immunity related to sepsis severity and mortality. We evaluated the clinical and prognostic significance of circulating PTX3 in the largest cohort ever reported of patients with severe sepsis or septic shock. Materials and methods: Plasma PTX3 was measured on days 1, 2 and 7 after randomization of 958 patients to albumin or crystalloids for fluid resuscitation in the multicentre Albumin Italian Outcome Sepsis (ALBIOS) trial. We tested the association of PTX3 and its changes over time with clinical severity, prevalent and incident organ dysfunctions, 90-day mortality and treatment. Results: PTX3 was high at baseline (72 [33–186] ng/mL) and rose with the sever...