OBJECTIVE: To examine how prenatal care providers responded to a new provincial policy of offering HIV testing to all prenatal patients, and to determine factors associated with self-reported high testing rates. DESIGN: Cross-sectional mailed survey. SETTING: Outpatient practices in three Ontario health-planning regions. PARTICIPANTS: Prenatal care providers: 784 family physicians, 200 obstetricians, and 103 midwives were sent questionnaires and were eligible to participate. MAIN OUTCOME MEASURES: Self-reported testing of 80% or more prenatal patients ("high testers") and associated practice characteristics, attitudes, and counseling practices. RESULTS: Response rate was 57% (622/1087): 43% of respondents were high testers. Family physicians were most likely and midwives least likely to be high testers. High testers tended to report that they had adequate knowledge of HIV testing, that HIV risk among their patients warranted testing all of them, and that testing should be routine. Encouraging women to test and not providing written information or choice were independently associated with high testing rates. CONCLUSION: Strongest predictors of high prenatal HIV testing rates were attitudes and practices that favoured a routine approach to testing and that placed little emphasis on informed consent.