This study of adolescent mothers sought to identify whether a single general question asked by phone or a detailed, vaccine-specific question asked in a self-report questionnaire best captured infant immunization status at 6 months postpartum, by comparing them with immunization record books. Responses to a global question about whether infants were up-to-date with immunizations more closely approximated immunization records than did vaccine-specific questionnaire items. High rates of "don't know" and blank responses in the questionnaire suggested respondents were unable to accurately answer detailed questions, even when successful at having their infant immunized. Analyses suggest that asking respondents about well-baby visits may be part of an alternative strategy for collecting accurate immunization data. (Contains 6 tables.)