Data were collected as part of a prospective cohort of 1,214 critically ill patients admitted to two hospitals in the Netherlands between January 2011 and June 2011. Eight observers assessed a random sample of 168 out of 554 patients who had experienced at least one infectious episode in the ICU. Each patient was assessed by two randomly selected observers who independently scored the source of infection (by affected organ system or site), the plausibility of infection (rated as none, possible, probable, or definite), and the most likely causative pathogen. Assessments were based on a post hoc review of all available clinical, radiological and microbiological evidence. The observed diagnostic agreement for source of infection was classified as partial (that is, matching on organ system or site) or complete (that is, matching on specific diagnostic terms), for plausibility as partial (two-point scale) or complete (four-point scale), and for causative pathogens as an approximate or exact pathogen match. Interobserver agreement was expressed as percentage agreement and as a kappa statistic.