THE EFFECT of birth order on birth weight of Saudi newborns has been evaluated. The study sample comprised 4498 Saudi newborns who were born in four major hospitals in Riyadh. For purposes of statistical analysis, birth weights were classified into four categories. These were low birth weight (<2500g), sub-optimal birth weight (2500-2999g), optimal birth weight (3000-3999g) and above optimal weight (≥4000g). Birth order was measured as the number of past pregnancies that have gone to viability and have been delivered regardless of the number of children involved. The results indicated that there is a linear relationship between birth order and birth weight, whereas the higher the birth order, the higher the proportion of optimal and above optimal birth weights. The chi-square test was significant at the probability level 0.001.