Objectives: Collagen cross-links are formed during the maturation process of bone matrix. They have been considered as valuable markers in some metabolic, endocrinologic, and neoplastic bone disorders. As an advantage, it can be measured in urine as well as in serum samples. However, the excretion characteristics remains controversial. Design and methods: We investigated urinary free deoxypyridinoline (f-Dpd) excretion in first-void urine samples and in 24-hour collections in healthy Turkish children. We also evaluated the possible correlations and gender-related differences in Dpd excretion between these sampling methods. Both urine samples of 62 subjects (aged from 31 to 120 months) were analyzed by Immulite chemiluminescent technique. Results: There were no remarkable differences in f-Dpd excretion between first-void and 24-hour urine samples, although f-Dpd values of the first-void samples were slightly higher (Dpd: creatinine, mean ± SD, 20.5 ± 5.8 nmol/mmol vs. 19.6 ± 5.6 nmol/mmol, respectively, p > 0.05). A strong linear correlation was found between 24-hour and first-void urine f-Dpd excretions (r = 0.77, p < 0.05). In addition, f-Dpd showed no gender-related differences between boys and girls in either 24-hour or first-void urine samples (p > 0.05). Conclusions: Because of difficulties in long-time urine collection in infants and young children, f-Dpd assessment in first-void single urine samples is an easy, safe, and non-invasive method. Copyright (C) 2000 The Canadian Society of Clinical Chemists.