We analyze 40 episodes of unsuspected hypoglycemia (glycemia < or = 3.30 mmol/l) in 36 in patients during seven months in a tertiary hospital. Only 22% of them were diabetics, the rest had other risk-factors such as malnutrition (47%), infections (47%), liver diseases (22%), renal failure (19%) or neoplasias (17%). Only 14% of the subjects had symptoms related to hypoglycemia, and only 27% received treatment. There were no significative differences between those patients over 65 years and the younger ones. Hypoglycemia was not the apparent cause of death in any of the patients, but hospital mortality of these patients was 25%, and it was related with the number of risk factors. We conclude that hypoglycemia in hospitalized patients is often unnoticed, as it appears with diseases other than diabetes, and that it is related with a high mortality in patients with severe diseases.