Aims: To obtain an understanding of the etiology of proportional dwarfism and endocrinopathies of Bloom’s syndrome (BS). Methods: Admission for 5-day periods to an NIH-supported Clinical Research Center of a randomly selected population of persons with BS (n = 11; mean age 11.5 years, range 9 months to 28.5 years) for clinical and genetic history-taking, physical examination, and endocrinological, gastroenterological and immunological testing. Results: An oral glucose tolerance test was performed in all participants. Impaired glucose tolerance was present in 4 individuals, insulin resistance was observed in 6 individuals, and previously unrecognized diabetes was found in 1. Growth hormone provocation was normal in the 10 individuals tested. Overnight frequent GH sampling was suggestive of neurosecretory dysfunction in 3. Compensated hypothyroidism was found in 2 participants. Lipid profile abnormalities were present in 5 of 10 individuals. Low immunoglobulin concentrations (IgG and/or IgM) were seen in all tested. Intestinal absorption by D-xylose and/or fecal fat measurement was normal in all individuals tested as well. Conclusion: Altered carbohydrate metabolism is very common in BS, and is present from childhood. BS dwarfism is not related to growth hormone deficiency or malabsorption. The basis for the growth restriction in BS remains to be elucidated.