Fungicides include chemicals that are known aneugens. The purpose of the present study was to investigate whether occupational exposure to these and other agricultural pesticides induces aneuploidy in human sperm. The contribution of lifestyle factors (smoking and alcohol consumption) to the frequency of aneuploid sperm was evaluated as well. The effects of age and sperm concentration were analyzed as confounders. Spermatozoa from 30 healthy farmers were studied before and after exposure to fungicides, using fluorescence in situ hybridization (FISH). Ten thousand spermatozoa were scored per semen sample to determine the disomy and diploidy frequencies for chromosomes 1 and 7. Exposure to fungicides was not associated with sperm aneuploidy. Smoking was significantly associated with sperm carrying an extra chromosome 1 and with diploid sperm as well as with the aggregate frequency of aneuploid sperm. Alcohol consumption, sperm concentration, and age showed inconsistent results before and after the season of exposure to fungicides. For low-level exposures, such as occupational exposures, the sensitivity of the sperm-FISH method may not be sufficient. The present study supports earlier ones showing that smoking can increase aneuploidy in human sperm.