BACKGROUND. This cross-sectional study was performed to determine the reference ranges for two bone turnover markers -aminoterminal propeptide of type I collagen (P1NP) and C-terminal telopeptide of type I collagen ( - CrossLaps, -CTX)- in normal postmenopausal Spanish women as determined in serum by automated methods. METHODS. A community-based population of 1080 healthy postmenopausal women was evaluated. Data regarding risk factors for osteoporosis and fractures were collected by means of a structured questionnaire. Fasting serum levels of P1NP, -CTX, 25-Hydroxivitamin D (25OHD), and intact parathyroid hormone (iPTH) were measured on the Elecsys 2010 automated analyzer (Roche). BMD at lumbar spine, femoral neck and total hip was determined by DXA. RESULTS. The mean age of subjects was 63±9. Logarithmic transformation of both markers was performed to allow for normal distributions. Mid-95% ranges for P1NP and -CTX were 19-100 ng/ml and 0.112-1.018 ng/ml, respectively. Mean values of P1NP (47.7±19.9 ng/ml) were similar to those previously determined by the manufacturer of the assays, whereas -CTX mean values (0.387± 0.197 ng/ml) were lower. Both markers were higher among osteoporotic women. CONCLUSIONS. Values obtained from this well-characterized population study provide reference ranges for serum automated P1NP and -CTX in normal Spanish postmenopausal women.