The authors used data from the AAMC Matriculating Student Questionnaire and Medical School Graduation Questionnaire to ascertain how closely the specialty or subspecialty choices of the 1991 and 1994 graduates of U.S. medical schools matched the preferences they had declared when they were matriculated; the extent to which these students strongly considered and then rejected choices that arose during medical school; and the graduation choices of the substantial number of students in both cohorts who were undecided about their careers when they entered medical school. Approximately 80% of the graduates in both classes rejected the specialty intentions they had declared when they began medical school. However, matriculation interests in the generalist specialties--family practice, general pediatrics, and general internal medicine--were more enduring for the 1994 cohort, while interests in the medical, surgical, and support specialties were less so. Large percentages of the 1991 and 1994 cohorts were undecided about their careers at matriculation (20.8% and 26.2%, respectively), and nearly the same proportions remained undecided at graduation. However, more of the graduates in the 1994 cohort who had initially been undecided reached decisions favoring one of the generalist specialties than was true for the 1991 cohort. Nearly half the 1994 graduates had strongly considered and then rejected an alternative to their matriculation interest that arose during medical school. Within the generalist specialties, both early and later interests in family practice were more durable than were those in general pediatrics and general internal medicine: for every student who retreated from tentative interest in family practice, another student's interest was reinforced or kindled.(ABSTRACT TRUNCATED AT 250 WORDS)