Selective attrition is a potential source of bias in longitudinal analyses. We addressed 3 types of attrition and found no evidence that attrition was different for individuals with low birth weight and for those with normal birth weight. In the first type of attrition, children born between1951 and1 968 (the birth cohorts we examined) may have been less likely to survive until 1968, when their families were first interviewed, if they had low birth weight