The growth and bone mineralization were studied in ten preterm infants fed human milk and 14 preterm infants fed cow's milk-based formula. After discharge from the hospital, at 42, 48, and 56 weeks' postmenstrual age, anthropometric measures of weight, length, occipital frontal circumference, mid-upper arm circumference, triceps, and subscapular skin folds were obtained. Blood was drawn for determinations of serum calcium, phosphorus, 25-hydroxyvitamin D, alkaline phosphatase, and albumin levels. Bone mineral analyses were performed by photon absorptiometry. Mean (+/- SD) gestational ages in nursing and formula-fed infants were similar (32.0 +/- 2.5 vs 31.5 +/- 1.5 weeks), as were their mean (+/- SD) birth weights (1.76 +/- 0.42 vs 1.52 +/- 0.30 kg). After hospitalization, both groups had similar rates of growth in weight, length, head circumference, mid-upper arm circumference, triceps, and subscapular skinfold thickness. The formula-fed group had higher serum phosphorus levels at 42 weeks, higher serum calcium levels at 48 weeks, and higher serum albumin concentrations at 56 weeks than the breast-fed group. By 56 weeks' postmenstrual age, the bone mineral content was higher in the formula-fed group. Our data suggest that after hospitalization, preterm infants fed their own mother's milk have similar growth patterns but a different bone mineralization rate compared with preterm infants fed a standard cow's milk-based formula.