When bone is resorbed, cross-linking amino acids from collagen type I (pyridinolines) are excreted in the urine as small peptides. The purpose of this cross-sectional study was to measure the urinary excretion of type I collagen bone degradation products in children and to correlate the results with growth velocity on a population basis. Spot urines from 1076 children and 24 adults were analyzed. The concentrations of cross-linked N-telopeptides of collage type I were measured using a new monoclonal antibody-based microtiter-plate assay, and normalized to creatinine. Age-related changes in cross-link excretion mirrored published standard growth velocity rates for males and females. The correlation coefficient between growth rates and cross-link excretion was 0.91. These results encourage more definitive longitudinal studies where growth rates and collagen cross-link excretion are correlated on an individual-patient basis.