To analyze possible early abnormalities in bone resorption in type 1 diabetes mellitus the urinary excretion of the collagen crosslinks pyridinoline and deoxypyridinoline was evaluated by immunoassay in 26 prepubertal diabetic patients (mean age 7.8 +/- 1.6 years, mean duration 3.0 +/- 1.1 years) and 46 healthy children (age 8.3 +/- 1.3 years). Relationships with growth parameters (height-standard deviation score, body mass index and height velocity during the year preceding the study) and metabolic control were sought. Longitudinal and ponderal growth was normal in diabetic children. Urinary collagen crosslink excretion was 88.4 +/- 25 nmol/mmol creatinine (median 86, range 44-146) in diabetic patients and 65.6 +/- 19 nmol/mmol creatinine (median 61, range 32-108) in controls (p = 0. 0002). It was positively influenced by diabetic status (beta = 20.5) and negatively by age (beta = -6.41), controlling by sex and BMI (p = 0.0001). A positive correlation was found between collagen crosslinks and blood glucose (r = 0.48, p = 0.01) or HbA1c levels (r = 0.44, p = 0.02) evaluated at the time of the study, while no significant correlation was found with the mean HbA1c values assessed in the last year or throughout the whole duration of diabetes. Collagen crosslink excretion was significantly increased in patients who presented worsening of their metabolic control in the last 3 months. No relationship was found with the duration of disease or growth parameters. In conclusion, the elevated urinary excretion of collagen crosslinks in diabetic children indicates that bone resorption may be disturbed. Poor metabolic control influences the increased rate of bone resorption and may expose growing diabetic patients to a risk of bone loss.