Context: Most association studies of bone-related biomarkers (BBMs) with bone mineral density (BMD) have been conducted in postmenopausal women. Objective: We tested whether the following BBMs were cross-sectionally associated with BMD among young adults: serum 1, 25-dihydroxy vitamin D (1,25(OH)2D), 25-hydroxy vitamin D (25 OHD), PTH, osteocalcin, bone-specific alkaline phosphatase (BAP), and urinary pyridinoline/urinary creatinine. Setting and Participants: We studied 319 individuals (134 women, 149 black, 24-36 years) recruited during 1992 through 1993 in Oakland, California. BMD was assessed with dual-energy x-ray absorptiometry. Linear regression models estimated the association between BMD and each BBM. Results: 1, 25(OH) 2D was inversely associated with all BMDs. 25 OHD was positively, and PTH in-versely, associatedwith lumbarspine, total hip, and whole-body BMD. BAP was inversely associated with left arm, right arm, and whole-body BMD but not with spine or hip BMD. Neither osteocalcin nor urinary pyridinoline/urinary creatinine was associated with BMD. When we placed all BBMs (including 1, 25(OH)2D) in one model, the pattern and magnitude of association was similar except for PTH, which was attenuated. The association of BMD and BBMs did not differ significantly by race or sex. Conclusions: In this cross-sectional study of healthy young men and women who had PTH levels considered normal in clinical practice, higher PTH was associated with lower BMD, particularly in weight-bearing sites (ie, spine and hip). The inverse association of 1, 25(OH)2D, together with the attenuation of PTH, suggests that the observed association of PTH is mediated by 1, 25(OH) 2D. BAP was inversely associated with arm BMD. BBMs can be important markers of skeletal activity in young adults, but their clinical role on bone health among this population is yet to be fully determined.