There are few studies on cancer risks among female farmers, particularly on breast cancer and cancer in female genital organs. We have conducted a cohort study of cancer risk among 50,682 women with occupations in agriculture according to the Swedish 1970 census. The cohort was followed up in the nationwide, population-based, Cancer-Environment Register from 1 January 1971 until death or until 31 December 1987. Expected number of cases was based on annual cancer incidence in five-year age groups. The standardized incidence ratio (SIR) was computed as the ratio between observed and expected number of cases. A total of 4,474 cases of cancer were observed in the cohort from 1971 until 1987 cf 5,273 expected, resulting in a significantly decreased SIR of 0.85 (95 percent confidence interval [CI] = 0.82-0.87). SIR for breast cancer was significantly decreased (0.83, CI = 0.78-0.88), as was the SIR for cervix uteri (0.40, CI = 0.31-0.50). For the other female genital organs, SIR was close to one. Other cancer sites with significantly decreased SIRs were: colon (0.90, CI = 0.81-1.00); rectum (0.86, CI = 0.74-1.00); lung (0.46, CI = 0.37-0.57); kidney (0.81, CI = 0.68-0.97); urinary organs (0.57, CI = 0.45-0.72); connective tissue and muscle (0.62, CI = 0.39-0.95); and non-Hodgkin's lymphomas (0.78, CI = 0.63-0.96).