The objective of this study was to examine the impact of changes in maternal age and parity distribution on birth weight. The study population included 7,786 single live births in 1977 and 8,671 single live births in 1987 delivered at 9 medical facilities in Pusan. Data were obtained from the delivery record. The proportion of infants born to the mothers of 25-29 years increased from 56.475 in 1977 to 65.1% in 1987 and the proportion to the mothers of 30-34 years increased from 18.8% in 1977 to 21.6% in 1987. In the same period, the proportions of 1st and 2nd birth order were increased from 56.9% and 28.8% to 59.9% and 36.8%, respectively. The proportion of infants born to the age group of ${leq}24;and;35{leq}$ years were decreased in 1987. The proportion of births of the third or higher birth order was decreased from 14.2% in 1977 to 3.3% in 1987. Low birth weight (<2500gm) incidence rate was 5.3% in 1977 and it was decreased to 4.0% in 1987. It was estimated that changes in maternal age-parity distribution accounted for 10.7% of the decreased in low birth weight incidence rate. Rest of the change (89.3%) was attributed to the reduction of age-parity specific low birth weight incidence rate. Application of the direct adjustment method was considered to be an adequate tool for evaluating the impact of family planning on neonatal health.