The traditional preference for sons may be the main hindrance to India's current population policy of two children per family. In this study, the effects of various sociodemographic covariates, particularly sex preference, on the length of the third birth interval are examined for the scheduled caste population in Assam, India. Life table and hazards regression techniques are applied to retrospective sample data. The analysis shows that couples having two surviving sons are less likely to have a third child than those without a surviving son and those with only one surviving son. Age at first marriage, length of preceding birth intervals, age of mother, and household income have strong effects on the length of the third birth interval.