BACKGROUND Hemolysis of red blood cells (RBCs) during blood bank storage is the most obvious manifestation of RBC storage system failure. However, its analysis is made difficult because the largest source of interunit difference is donor specific. Availability of data from national blood systems on large numbers of RBC units used for internal quality control (QC) purposes and stored and processed in uniform ways permits statistical analysis. METHODS Measures of hemolysis during and at the end of storage on randomly selected donor units observed for QC purposes were obtained from four national blood systems. Groups of these measures from units that had undergone similar processing and storage were sorted to create histograms and the histograms were compared statistically. RESULTS A total of 14,087 measures were obtained under seven storage conditions, including more than 12,000 measures made in a single country under four closely related conditions. Distributions of percent hemolysis are skewed normal and outliers are random. Additive solutions appear to be equivalent, except that the 42 mmol/L mannitol in AS-1 reduces hemolysis compared to conventional 30 mmol/L mannitol in saline, adenine, glucose, and mannitol. Increasing storage from 35 to 42 days increased measured hemolysis by 30% and leukoreduction decreased it by 53%. CONCLUSIONS Large national data sets provide useful information about the distribution of hemolysis at the end of RBC storage. This information can aid blood storage system development and regulatory science.