The associations among certain allergic disorders, atopy upon skin-prick testing, and specific cancers were evaluated in a prospective study. Information regarding history of asthma and hay fever was collected by questionnaire from 3,308 cancer-free participants in the 1981 Busselton Health Survey. A subset of 1,005 participants also underwent skin-prick testing. The cohort was followed for a new diagnosis of cancer or death until the end of 1999. Cox proportional hazards regression analysis was used to estimate adjusted hazard ratios (relative risks) for breast, prostate, colorectal, lung, and hematologic cancers and melanoma. Having a skin reaction to house dust mites nearly tripled the risk of prostate cancer (relative risk=2.90, 95% confidence interval: 1.26, 6.68). History of asthma and hay fever were associated with a trend toward a reduced risk of colorectal cancer and increased risk of leukemia, but these results were not statistically significant. Hay fever was associated with melanoma risk in men but not in women. No association was found between breast and lung cancers and allergic disorders or atopy.