Life table analysis is applied to data from the Pakistan Fertility Survey (1975) to examine the effects on birth spacing of a number of socioeconomic variables. Women of more modern backgrounds seem to space their families more closely, but differ little in achieved family size from the more traditional groups. Important factors are age at marriage, age at first birth, province of residence, and whether the woman had ever used contraception. Multivariate analysis taking into account interaction between variables shows that education, urban-rural residence, and province exert independent effects, and so does the cohort of the mother. But the variable with the strongest effect on length of interval, other than that from marriage to first birth, is duration of breast-feeding.