Flax (Linum usitatissimum L.) is being evaluated as a platform crop for genetically engineered (GE) novel oils but it must be able to coexist with non-GE flax without causing market harm. The GE flax volunteers are a potential source of gene flow via pollen and seed. Field experiments in 2005 and 2006 quantified emergence periodicity of volunteer flax in direct seeded and conventionally tilled fields. Germination and emergence rates of naked seeds and seed retained in flax bolls were compared in laboratory and greenhouse trials. Lastly, 20 commercial flax fields were surveyed to quantify population size and persistence of volunteer flax for 3 yr following the flax crop. Volunteer flax emergence ranged from 31 to 4597 plants m-2, the year following flax crops. Emergence was slower in direct seeded fields compared to conventionally tilled with 50% emergence (E50) occurring at 340 and 228 growing degree days (GDD), respectively in 2005 and 297 and 236, respectively in 2006. The E50 occurred after crop emergence and before in-crop herbicides are normally applied. Greenhouse experiments confirmed that emergence of volunteer flax may be prolonged because seeds retained in flax bolls are protected from germination. In surveyed commercial fields, flax volunteer populations declined rapidly between the first and second year, but continued to emerge in some fields 3 yr following flax production. Field surveys confirmed the relatively slow emergence of volunteer flax, with the highest volunteer flax density observed in the survey period before in-crop herbicide application. Few flax volunteers set seeds in commercial fields and are, therefore, unlikely to contribute to population persistence. Volunteer flax requires effective control in the year following the crop to reduce the potential for pollen- and seed-mediated gene flow.