Various factors led to delays of several months to several years in the diagnosis of pernicious anemia in 11 patients, occasionally with serious consequences. These cases illustrate that earlier diagnosis is possible with closer attention to abnormal results of common tests. Macrocytosis, detected by high mean corpuscular volume, often preceded anemia but was not investigated, especially when anemia was only slight. Several cases demonstrated that vitamin B12 deficiency may initially produce only a mild macrocytic anemia, which is maintained for a long period before a rapid worsening supervenes; the reason for the latter acceleration of anemia is unknown. Most serious was the evidence that mild anemias are often ignored. Stricter attention to the established limits of normal hemoglobin values is required. These aspects of physician performance have implication for the recognition of all anemias.