This study aimed to determine differences in the rates of growth, endocrine- and calcium-related abnormalities in the various thalassemia syndromes in North America treated with current therapies. Medical history, physical examinations and blood and urine collections were obtained from patients with all thalassemia syndromes age 6 years and older in the Thalassemia Clinical Research Network. 361 subjects, 49% male, mean age 23.2 years (range 6.1-75 years) were studied. Approximately 25% of children and adults, regardless of the thalassemia syndrome, had short stature. Overall growth in children was mildly affected. Final height was close to midparental height (z = -0.73 +/- 1.24). Patients with beta thalassemia major (TM) had higher rates of hypogonadism, multiple endocrinopathies, worse hyperglycaemia, subclinical hypoparathyroidism and hypercalciuria. Hypogonadism remained the most frequent endocrinopathy and was frequently under-treated. 12.8% of the subjects had 25 vitamin D concentrations less than 27 nmol/l and 82% less than 75 nmol/l, regardless of the thalassemia syndrome. Adolescents had lower 25 vitamin D levels than children and adults. Compared to patients with other thalassemia syndromes, those with beta TM suffered from higher rates of multiple endocrinopathies, abnormal calcium metabolism and hypercalciuria. Vitamin D abnormalities were high among adolescents.