The erythrocyte sedimentation rate (ESR) is a time-honored blood test, which assesses the degree of erythrocyte aggregation by acute phase proteins such as fibrinogen and immunoglobulins. Various intrinsic factors may influence the ESR, among them polycytemia, microcytosis or fibrinogen consumption lead to a decreased ESR, while anemia, macrocytosis or hypoalbuminemia lead to an increased ESR. The ESR still is a very valid test for the diagnosis of certain chronic diseases (polymyalgia, rheumatoid arthritis, multiple myeloma, septic arthritis and ostemyelitis) and the follow-up of certain chronic diseases (polymyalgia rheumatica, systemic lupus erythematodes, chronic infections, prostatic cancer, and Hodgkin's disease). In acute disease states and their monitoring C-reactive protein and eventually procalcitonin are the tests of choice. The ESR should not be used for screening and check-up examinations in asymptomatic patients.