The occurrence of adverse events temporally associated with diphtheria and tetanus toxoids and pertussis vaccine (DTP) has led to consideration of a delay in the schedule of initial vaccination. We developed an inferential model estimating the changes in pertussis- and DTP-associated health outcomes that might occur if initial DTP administration were delayed from 2,4, and 6 months to 8,10, and 12 months of age. An additional 636 cases of pertussis—115 of which would be associated with complications, including two encephalopathies—were projected to occur under the proposed as compared to the current schedule. Adverse medical events attributable to the vaccine were assumed to remain unchanged following the change in schedule. We projected 353 fewer chance associations with sudden infant death syndrome but 1311 more chance associations between DTP and seizures. These estimates suggest that the current schedule of vaccinating infants at 2, 4, and 6 months of age is causally associated with less morbidity and should be continued.