The Vietnamese are the fastest-growing Asian/Pacific Islander ethnic group in California. Data from Vietnam and elsewhere suggest that cervical cancer and breast cancer are major contributors to cancer morbidity and mortality among Vietnamese women. However, little is known about the cancer knowledge and screening practices of Vietnamese women. Using a structured 57-item written questionnaire, we conducted a mailed survey of 400 randomly selected Vietnamese adult women in San Francisco. Overall, 107 women responded (31%). Of the respondents, 54 (52%) indicated that there was little one could do to prevent cancer. More than a third (39%) thought that breast or cervical cancer could be caused by poor hygiene, and about one-third (29%) thought that these cancers could be contagious. Although virtually all (97%) had heard of cancer, one-third did not know that a breast lump could be a sign of breast cancer (37%) or that abnormal vaginal bleeding could be a sign of cervical cancer (39%). Many (55%) did not know that family history was a risk factor for breast cancer and three-fourths (74%) did not know that having multiple sexual partners was a risk factor for cervical cancer. Fourteen (13%) had not heard of breast self-examination. Of 31 women aged > or = 40, 10 (34%) had never had a mammogram, and of 92 women aged > or = 18, 50 (54%) had never had a Papanicolaou test.(ABSTRACT TRUNCATED AT 250 WORDS)