Asthma and related factors were assessed by mailed questionnaires among 2041 young adult participants in a smoking prevention project in California in 1993. Hispanics had lower prevalence of physician-reported asthma when compared to blacks and whites. Blacks were significantly more likely to be hospitalized or visit emergency rooms because of asthma or wheezing. After adjusting for sex, race, and educational level, family history of asthma was strongly associated with subjects' asthma (odds ratio = 3.1, 95% CI: 2.4-4.3 for physician-reported asthma; OR = 3.3, 95% CI: 2.4-4.5 for current asthma). Exposure to parental smoking (both parents smoked more than half a pack of cigarettes a day) during childhood (reported when participants were in grade 7) was significantly associated with physician-reported asthma (OR = 2.9, 95% CI: 1.6-5.6) and current asthma (OR = 3.3, 95% CI: 1.7-6.4). The study also found that self-reported mold growth at home was significantly associated with asthma (OR = 2.0, 95% CI: 1.2-3.2). After adjusting for cigarette smoking and demographic variables, use of crack cocaine was marginally significantly associated with current asthma (OR = 2.3, 95% CI: 1.0-5.2), but not with physician-reported asthma (OR = 1.5, 95% CI: 0.7-3.3).