Weeds are a major contributing factor to crop yield loss. Weed control is regularly practiced during the growing season, with many growers making a conscious effort to minimise weed-seed return to the soil seedbank during the cropping program. However, growers may be unintentionally introducing weed seeds through sowing of contaminated crop seed. Using samples of crop seed obtained from 29 growers across two Western Australian grain-growing regions, 81 samples were hand-cleaned to determine weed-seed contamination levels. Of those samples, 41% were weed-free, and in the remaining 59%, the main contaminant was Lolium rigidum (annual ryegrass), occurring in 49% of contaminated samples. Crop type and cleaning method had significant effects on the level of weed-seed contamination, with barley having higher levels of contamination than other crops, and professional contractors providing lower contamination than other methods of cleaning. However, any seed-cleaning method provided significantly cleaner grain samples than no seed cleaning. This study established that crop-seed contamination was evident on Western Australian farms and that growers may be unintentionally sowing weed seeds with their crops. Seed cleaning combined with judicious paddock selection and weed-seed removal during the growing season can lead to weed-free crop seed.