OBJECTIVE To assess the data quality of septicemia and sepsis registration in a hospital discharge registry in the County of Northern Jutland, Denmark. METHODS Comparison of data from the discharge registry of an 880-bed, public, urban hospital in the County of Northern Jutland with data from a computerized bacteremia database at the regional department of clinical microbiology. METHODS Urban hospital with approximately 45,000 admissions per year. METHODS The study included 406 episodes of bacteremia in the bacteremia database and 83 discharges with the diagnosis of septicemia registered in the hospital discharge registry between January 1, 1994, and December 31, 1994. METHODS None. RESULTS Eighteen episodes were registered in both the hospital discharge registry and the bacteremia database. Using the bacteremia database as reference standard, the sensitivity for the diagnosis of septicemia in the hospital discharge registry was 4.4% (18/406; 95% confidence intervals [CI95, 2.4%-6.4%]). By review of hospital records, we estimated the positive predictive value of septicemia registration in the hospital discharge registry as 21.7% (18/83; CI95, 12.8%-30.5%). No blood culture had been obtained in 44.4% (36/81; CI95, 33.6%-55.3%) of the cases with a discharge diagnosis of septicemia. In 33.3% (27/81; CI95, 23.1%-43.6%), the discharge diagnosis of septicemia was given, although blood cultures were negative. CONCLUSIONS The hospital discharge registry revealed numerous misclassifications, and the system was found not suited for surveillance of, or research in, bacteremia at present.