Aim: To determine fungal genera, Aspergillus and Fusarium species and aflatoxin B-1 (AFB(1)), zearalenone (ZEA), deoxynivalenol (DON), fumonisin B-1 (FB1) contamination from pre- and postfermented corn silage produced in the most important region of Argentina where silage practice is developed. Methods and Results: Sampling of corn silos was performed manually through silos in transects at three levels: upper, middle and low sections. AFB(1) and FB1 were quantified by high-performance liquid chromatography, zearalenone by enzyme-linked immunosorbent assay and DON by gas chromatography. Over 90% of the samples showed counts higher than 1 x 10(4) CFU g(-1). Aspergillus flavus and Fusarium verticillioides were the prevalent species. Some tested samples were contaminated with AFB(1), ZEA, DON and FB1. Conclusions: This study demonstrates the presence of fungi and AFB(1), ZEA, DON and FB1 contamination in corn silage in Argentina. Significance and Impact of the Study: This manuscript makes a contribution to the knowledge of mycotoxins in Argentinean silage in particular because the environmental conditions in this country differ from those of most reports. The comparison of pre- and postfermentation silage is also outstanding. Therefore, information on fungi and mycotoxins present in silage - an increasingly popular commodity - is useful to estimate potential risk for animal and human health.